Showing papers on "Nucleation published in 2006"
TL;DR: In this article, the up-conversion fluorescence intensity of hexagonal-phase NaYF4:Yb,Er nanocrystals was shown to be much higher than that of other cubic-phase nanocrystal, including the ones in this work.
Abstract: IR-to-visible up-conversion fluorescent nanocrystals of hexagonal-phase NaYF4:20 %Yb,2 %Er and NaYF4:20 %Yb,2 %Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF3COO)3Y, (CF3COO)3Yb, and (CF3COO)3Er/(CF3COO)3Tm in oleylamine at 330 °C. The average particle size is 10.5 ± 0.7 nm (from random measurements of 200 particles from five transmission electron microscopy images) and 11.1 ± 1.3 nm (from dynamic-light-scattering measurements). The up-conversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic-phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal-phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes.
755 citations
TL;DR: In this paper, the authors spectroscopically monitored a nucleation process in the self-assembly of p-conjugated molecules into helical supramolecular fibrillar structures.
Abstract: Hierarchical self-assembly offers a powerful strategy for producing molecular nanostructures. Although widely used, the mechanistic details of self-assembly processes are poorly understood. We spectroscopically monitored a nucleation process in the self-assembly of p-conjugated molecules into helical supramolecular fibrillar structures. The data support a nucleation-growth pathway that gives rise to a remarkably high degree of cooperativity. Furthermore, we characterize a helical transition in the nucleating species before growth. The self-assembly process depends strongly on solvent structure, suggesting that an organized shell of solvent molecules plays an explicit role in rigidifying the aggregates and guiding them toward further assembly into bundles and/or gels.
747 citations
TL;DR: A very rapid technique for the production of metal-organic frameworks (MOF) using a conventional microwave to nucleate crystal growth that used to take hours or days can now be completed in 30 s to 2 min.
Abstract: This paper describes a very rapid technique for the production of metal−organic frameworks (MOF). The method uses a conventional microwave to nucleate crystal growth. A MOF synthesis that used to take hours or days can now be completed in 30 s to 2 min. The yield goes from ∼30% to over 90%. Novel MOFs can be made, since the growth process is no longer dependent on the walls or dust particles for nucleation. Particle sizes have a narrower distribution. Further, the particle size can be controlled by varying the precursor concentration.
606 citations
TL;DR: A new aggregation mechanism is proposed in which aggregation is triggered by heterogeneous nucleation, which may prove to be of great value in reproducibly synthesizing nanoparticles with well-controlled sizes and shapes and in effectively preventing aggregation in chemical, pharmaceutical, and materials production processes.
Abstract: The aggregation of nanoparticles during synthesis, particularly the effect of mechanical agitation, is investigated from a viewpoint of nucleation using a conjugated polymer, polyaniline, as an example. Homogeneous nucleation of polyaniline results in nanofibers, while heterogeneous nucleation leads to granular particulates. Mechanical agitation, which is a common method for disrupting aggregates, instead dramatically triggers aggregation during the synthetic process and favors the formation of granular particulates. Correlating the shape and aggregation of polyaniline nanoparticles with the mode of nucleation, a new aggregation mechanism is proposed in which aggregation is triggered by heterogeneous nucleation. The mechanism may be quite general as indicated by experiments with other materials such as silica nanoparticles. Highly dispersible polyaniline nanofibers can now be reproducibly prepared from a conventional reaction simply by not mechanically agitating the reaction and carrying it out at an elevated temperature. This work may prove to be of great value in reproducibly synthesizing nanoparticles with well-controlled sizes and shapes and in effectively preventing aggregation in chemical, pharmaceutical, and materials production processes.
508 citations
TL;DR: In this paper, the authors present an activation theory, which can explain the observed slope of particle formation, which predicts that the critical cluster contains one to two sulphuric acid molecules.
Abstract: According to atmospheric observations new particle formation seems to be a function of sulphuric acid concentration to the power from one to two. The nucleation theorem then predicts that the critical cluster contains one to two sulphuric acid molecules. However, existing nucleation theories predicts that the power is more (or equal) than 2. Here we present an activation theory, which can explain the observed slope. In cluster activation the clusters containing one sulphuric acid molecule will activate for further growth due to heterogeneous nucleation, heterogeneous chemical reactions including polymerization or activation of soluble clusters. In the activation process organic vapours are typically needed as condensing agents.
454 citations
TL;DR: The latest attempts to describe the sometimes complex phase equilibria of fats using fundamental relationships for chemical potential that have so far been applied to individual species in melts of unary, binary and ternary systems are reviewed.
427 citations
TL;DR: In this paper, the authors investigated the formation and early growth of atmospheric secondary aerosol particles building on atmospheric measurements and found that new particle formation seems to be a function of the gaseous sulphuric acid concentration to the power from one to two.
Abstract: . We have investigated the formation and early growth of atmospheric secondary aerosol particles building on atmospheric measurements. The measurements were part of the QUEST 2 campaign which took place in spring 2003 in Hyytiala (Finland). During the campaign numerous aerosol particle formation events occurred of which 15 were accompanied by gaseous sulphuric acid measurements. Our detailed analysis of these 15 events is focussed on nucleation and early growth (to a diameter of 3 nm) of fresh particles. It revealed that new particle formation seems to be a function of the gaseous sulphuric acid concentration to the power from one to two when the time delay between the sulphuric acid and particle number concentration is taken into account. From the time delay the growth rates of freshly nucleated particles from 1 nm to 3 nm were determined. The mean growth rate was 1.2 nm/h and it was clearly correlated with the gaseous sulphuric acid concentration. We tested two nucleation mechanisms – recently proposed cluster activation and kinetic type nucleation – as possible candidates to explain the observed dependences, and determined experimental nucleation coefficients. We found that some events are dominated by the activation mechanism and some by the kinetic mechanism. Inferred coefficients for the two nucleation mechanisms are the same order of magnitude as chemical reaction coefficients in the gas phase and they correlate with the product of gaseous sulphuric acid and ammonia concentrations. This indicates that besides gaseous sulphuric acid also ammonia has a role in nucleation.
421 citations
TL;DR: Observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy suggest that interfacial free energy is the crucial parameter for premelts in colloidal and atomic-scale crystals.
Abstract: Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.
417 citations
TL;DR: It was found that each polymer was able to significantly decrease the nucleation rate of amorphous felodipine even at low concentrations (3-25% w/w), and hydrogen bonding interactions were formed between felodIPine and each of the polymers.
387 citations
TL;DR: Caupin et al. as mentioned in this paper reviewed the experimental work on cavitation in water, focusing on the determination of the ultimate degree of metastability at which liquid water can exist.
379 citations
TL;DR: In this article, a plethora of relevant experimental results on internal homogeneous crystal nucleation in silicate glasses obtained in the last four decades, and their analyses in the framework of the classical nucleation theory (CNT) are outlined.
Abstract: We review a plethora of relevant experimental results on internal homogeneous crystal nucleation in silicate glasses obtained in the last four decades, and their analyses in the framework of the classical nucleation theory (CNT). The basic assumptions and equations of CNT are outlined. Particular attention is devoted to the analysis of the properties of the critical nuclei, which, to a large extent, govern nucleation kinetics. The main methods employed to measure nucleation rates are described and the possible errors in the determination of the crystal number density (and, correspondingly, in nucleation rates) are discussed. The basic regularities of both time and temperature dependencies of nucleation rates are illustrated by numerous experimental data. Experimental evidence for a correlation between maximum nucleation rates and reduced glass transition temperatures is presented and theoretically justified. Special attention is given to serious problems that arise in the quantitative description of nucleation rates when using the CNT, for instance: the dramatic discrepancy between calculated and measured nucleation rates; the high value of the crystal nuclei/melt surface energy, σcm, if compared to the expected value estimated via Stefan’s rule; the increase of σcm with increasing temperature; and the discrepancies between the values of the surface energy and the time-lag for nucleation when independently estimated from nucleation and growth kinetics. The analysis of the above mentioned problems leads to the following conclusion: in contrast to Gibbs’ description of heterogeneous systems underlying CNT, the bulk thermodynamic properties of the critical nuclei generally differ from those of the corresponding macro-phase resulting simultaneously in significant differences of the surface properties as compared with the respective parameters of the planar interfaces. In particular, direct experimental evidence is presented for compositional changes of the crystal nuclei during formation of the critical nuclei and their growth from critical to macro-sizes. In addition, detailed examinations of crystal nucleation and growth kinetics show a decrease of both the thermodynamic driving force for nucleation and of the critical nuclei/liquid interfacial energy, as compared with the respective properties of the macro-phase. However, despite significant progress in understanding crystal nucleation in glasses in the past four decades, many problems still exist and this is likely to remain a highly interesting subject for both fundamental and applied research for a long time.
TL;DR: In this article, the leading and trailing dislocations are nucleated at different regions within a grain boundary or even different grain boundaries, and propagation is hindered by a pinning-depinning mechanism influenced by the relative orientation between the Burgers vector and the ledge geometry of the grain boundary.
TL;DR: A site-specific sequential nucleation and growth route to the systematic building of hierarchical, complex, and oriented ZnO micro/nanostructures in solution nanosynthesis.
Abstract: Here we report a site-specific sequential nucleation and growth route to the systematic building of hierarchical, complex, and oriented ZnO micro/nanostructures in solution nanosynthesis. Structures and morphologies of the products were confirmed by results from X-ray diffraction and scanning electron microscopy studies. The organic structure-directing agents (SDAs), diaminopropane and citrate, are found to play different roles in controlling the evolution of these new morphologies. Through the selective adsorptions of SDAs on different crystal facets of the primary ZnO rods, we have alternated the hierarchical growth of secondary and tertiary new complex nanostructures. Roles of the SDA concentration, nucleation time, and growth kinetics in the solution hierarchical ZnO nanosyntheses have all been systematically investigated.
TL;DR: A fundamental understanding of particle size control in antisolvent precipitation is beneficial for designing mixing systems and surfactant stabilizers for forming nanoparticles of poorly water soluble drugs with the potential for high dissolution rates.
Abstract: Organic itraconazole (ITZ) solutions were mixed with aqueous solutions to precipitate sub-300 nm particles over a wide range of energy dissipation rates, even for drug loadings as high as 86% (ITZ weight/total weight). The small particle sizes were produced with the stabilizer poloxamer 407, which lowered the interfacial tension, increasing the nucleation rate while inhibiting growth by coagulation and condensation. The highest nucleation rates and slowest growth rates were found at temperatures below 20 degrees C and increased with surfactant concentration and Reynolds number (Re). This increase in the time scale for growth reduced the Damkohler number (Da) (mixing time/precipitation time) to low values even for modest mixing energies. As the stabilizer concentration increased, the average particle size decreased and reached a threshold where Da may be considered to be unity. Da was maintained at a low value by compensating for a change in one variable away from optimum conditions (for small particles) by manipulating another variable. This tradeoff in compensation variables was demonstrated for organic flow rate vs Re, Re vs stabilizer concentration, stabilizer feed location (organic phase vs aqueous phase) vs stabilizer concentration, and stabilizer feed location vs Re. A decrease in the nucleation rate with particle density in the aqueous suspension indicated that secondary nucleation was minimal. A fundamental understanding of particle size control in antisolvent precipitation is beneficial for designing mixing systems and surfactant stabilizers for forming nanoparticles of poorly water soluble drugs with the potential for high dissolution rates.
TL;DR: A new approach for calculating reaction coordinates in complex systems based on transition path sampling and likelihood maximization is presented, which requires fewer trajectories than a single iteration of existing procedures and applies to both low and high friction dynamics.
Abstract: We present a new approach for calculating reaction coordinates in complex systems. The new method is based on transition path sampling and likelihood maximization. It requires fewer trajectories than a single iteration of existing procedures, and it applies to both low and high friction dynamics. The new method screens a set of candidate collective variables for a good reaction coordinate that depends on a few relevant variables. The Bayesian information criterion determines whether additional variables significantly improve the reaction coordinate. Additionally, we present an advantageous transition path sampling algorithm and an algorithm to generate the most likely transition path in the space of collective variables. The method is demonstrated on two systems: a bistable model potential energy surface and nucleation in the Ising model. For the Ising model of nucleation, we quantify for the first time the role of nuclei surface area in the nucleation reaction coordinate. Surprisingly, increased surface area increases the stability of nuclei in two dimensions but decreases nuclei stability in three dimensions.
TL;DR: It is demonstrated that the flow profile over the sample mediates the supply of reactants to the catalyst and that pretreatment using H2 significantly affects the initial activity of the catalyst.
Abstract: We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt transitions between areas of micrometer-thick tangled CNT films and millimeter-scale aligned CNT structures are manipulated by changing the duration of pretreatment by H2/Ar prior to introduction of C2H4 and by changing the configuration of the substrate sample in the furnace tube. This demonstrates that the flow profile over the sample mediates the supply of reactants to the catalyst and ...
TL;DR: It is suggested that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.
Abstract: We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350 °C by catalytic chemical vapor deposition from undiluted C2H2. NH3 or H2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.
HGST1
TL;DR: Simulation of coercivity and SFD versus element size allow the distribution of intrinsic anisotropy to be quantified in highly exchanged coupled thin films where the reversal mechanism is one of nucleation followed by rapid domain wall motion.
Abstract: We demonstrate that the switching field distribution (SFD) in arrays of 50 nm to $5\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ $\mathrm{Co}/\mathrm{Pd}$ elements, with perpendicular anisotropy, can be explained by a distribution of intrinsic anisotropy rather than any fabrication related effects. Further, simulations of coercivity and SFD versus element size allow the distribution of intrinsic anisotropy to be quantified in highly exchanged coupled thin films where the reversal mechanism is one of nucleation followed by rapid domain wall motion.
TL;DR: In this article, the role of sul- phuric acid in particle formation and growth was investigated in the QUEST III and BACCI/QUEST IV campaigns in Heidelberg and Hyyti, respectively.
Abstract: This study investigates the connections between atmospheric sulphuric acid and new particle formation dur- ing QUEST III and BACCI/QUEST IV campaigns. The campaigns have been conducted in Heidelberg (2004) and Hyyti¨ al¨ a (2005), the first representing a polluted site sur- rounded by deciduous forest, and the second a rural site in a boreal forest environment. We have studied the role of sul- phuric acid in particle formation and growth by determin- ing 1) the power-law dependencies between sulphuric acid ((H2SO4)), and particle concentrations (N3 6) or formation rates at 1 nm and 3 nm (J1 and J3); 2) the time delays be- tween (H2SO4) and N3 6 or J3, and the growth rates for 1- 3 nm particles; 3) the empirical nucleation coefficients A and K in relations J1=A(H2SO4) and J1=K(H2SO4) 2 , respec- tively; 4) theoretical predictions for J1 and J3 for the days when no significant particle formation is observed, based on the observed sulphuric acid concentrations and conden- sation sinks. In both environments, N3 6 or J3 and (H2SO4) were linked via a power-law relation with exponents typi- cally ranging from 1 to 2. The result suggests that the clus- ter activation theory and kinetic nucleation have the potential to explain the observed particle formation. However, some differences between the sites existed: The nucleation coeffi- cients were about an order of magnitude greater in Heidel- berg than in Hyyti¨¨ conditions. The time lags between J3 and (H2SO4) were consistently lower than the corresponding
TL;DR: In this article, an active:elastic/plastic inactive anode system was proposed to better understand the mechanism of capacity retention and the ultimate failure mode of a model brittle active-elastic and/or plastic inactive system, and the films were subjected to in situ adhesion tests.
Abstract: Amorphous silicon thin films deposited on copper foil have been observed to exhibit near theoretical capacity for a limited number of cycles. The films, however, eventually delaminate, leading to failure of the anode. In order to better understand the mechanism of capacity retention and the ultimate failure mode of a model brittle active:elastic/plastic inactive anode system, the films were subjected to in situ adhesion tests while observing the film surface using scanning electron microscopy. Atomic force and transmission electron microscopy, and electrochemical cycling were conducted to analyze the emerging morphology of the films during cycling. The adhesion of the as-deposited Si film to the Cu substrate was measured to ∼7.7 J/m 2 , reflecting a weak interface adhesion strength. Plastic deformation of the underlying Cu substrate combined with a ratcheting mechanism is proposed to occur in the Si:Cu system, with delamination failure mode occurring only after the formation of an interface imperfection. From the analysis of slow rate cycling experiments, nucleation of a lithium compound based on the interdiffusion of Si and Cu is identified as the most probable cause of the ultimate delamination failure of the deposited film.
TL;DR: In this article, the electrodeposition and surface morphology of aluminium on tungsten (W) and aluminium (Al) electrodes from 2 −: 1 molar ratio AlCl 3 -[EMIm]Cl ionic liquids were investigated.
Abstract: The electrodeposition and surface morphology of aluminium on tungsten (W) and aluminium (Al) electrodes from 2 : 1 molar ratio AlCl 3 –[EMIm]Cl ionic liquids were investigated. Analyses of the chronoamperograms indicate that the deposition process of aluminium on W substrates was controlled by instantaneous nucleation with diffusion-controlled growth, while the deposition processes of aluminium on Al electrodes were found to be associated with kinetic limitations. Constant potential deposition experiments showed that the electrodeposits obtained on both W and Al electrodes between − 0.10 and − 0.40 V (vs. Al(III)/Al) are dense, continuous and well adherent. Dense aluminium deposits were also obtained on Al substrates using constant current deposition between 10 and 70 mA/cm 2 , and the current efficiency was found to be dependent of the current density varying from 85% to 100%.
TL;DR: In this article, the synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes and the main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the surface energy.
Abstract: The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes. The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy.
TL;DR: Experimental evidence is presented of a well defined decoupling of transport properties (the self-diffusion coefficient and the average translational relaxation time) which implies the breakdown of the Stokes–Einstein relation, and reflects the characteristics of the recently observed dynamic crossover between the two dynamical behaviors known as fragile and strong.
Abstract: By confining water in nanopores, so narrow that the liquid cannot freeze, it is possible to explore its properties well below its homogeneous nucleation temperature TH≈ 235 K. In particular, the dynamical parameters of water can be measured down to 180 K, approaching the suggested glass transition temperature Tg≈ 165 K. Here we present experimental evidence, obtained from Nuclear Magnetic Resonance and Quasi-Elastic Neutron Scattering spectroscopies, of a well defined decoupling of transport properties (the self-diffusion coefficient and the average translational relaxation time), which implies the breakdown of the Stokes–Einstein relation. We further show that such a non-monotonic decoupling reflects the characteristics of the recently observed dynamic crossover, at ≈225 K, between the two dynamical behaviors known as fragile and strong, which is a consequence of a change in the hydrogen bond structure of liquid water.
TL;DR: It is demonstrated that a hydroxylated surface enhances Ca-P nucleation and growth relative to other surfaces, thereby supporting the concept of its beneficial effect on bone tissue formation and growth.
TL;DR: In this article, the effects of an inlet pressure restrictor and fabricated nucleation sites are evaluated as a means of stabilizing the flow boiling process and avoiding the backflow phenomenon.
Abstract: The flow boiling process suffers from severe instabilities induced due to nucleation of vapor bubbles in a superheated liquid environment in a minichannel or a microchannel. In an effort to improve the flow boiling stability, several modifications are introduced and experiments are performed on 1054197 m parallel rectangular microchannels (hydraulic diameter of 332 m) with water as the working fluid. The cavity sizes and local liquid and wall conditions required at the onset of nucleation are analyzed. The effects of an inlet pressure restrictor and fabricated nucleation sites are evaluated as a means of stabilizing the flow boiling process and avoiding the backflow phenomenon. The results are compared with the unrestricted flow configurations in smooth channels. DOI: 10.1115/1.2165208
TL;DR: In Al–Zr–Sc alloys, atomic simulations based on first-principle calculations combined with various complementary experimental approaches working at different scales reveal a strongly inhomogeneous structure of the precipitates: the precipitate core is mostly Sc-rich, whereas the external shell is Zr-rich.
Abstract: One usual way to strengthen a metal is to add alloying elements and to control the size and the density of the precipitates obtained. However, precipitation in multicomponent alloys can take complex pathways depending on the relative diffusivity of solute atoms and on the relative driving forces involved. In Al-Zr-Sc alloys, atomic simulations based on first-principle calculations combined with various complementary experimental approaches working at different scales reveal a strongly inhomogeneous structure of the precipitates: owing to the much faster diffusivity of Sc compared with Zr in the solid solution, and to the absence of Zr and Sc diffusion inside the precipitates, the precipitate core is mostly Sc-rich, whereas the external shell is Zr-rich. This explains previous observations of an enhanced nucleation rate in Al-Zr-Sc alloys compared with binary Al-Sc alloys, along with much higher resistance to Ostwald ripening, two features of the utmost importance in the field of light high-strength materials.
TL;DR: This work probes electrochemical nucleation and growth of individual nanoclusters in real time by combining current-time measurements with simultaneous video imaging and describes a significant revision to conventional models that can explain the results.
Abstract: Electrochemical techniques are used widely for the fabrication of nanostructured materials, yet a quantitative understanding of nucleation and growth remains elusive. Here we probe electrochemical nucleation and growth of individual nanoclusters in real time by combining current-time measurements with simultaneous video imaging. We show discrepancies between the growth kinetics measured for individual nanoclusters and the predictions of models, and we describe a significant revision to conventional models that can explain the results. This improved understanding of nucleation and growth allows a more quantitative approach to the electrochemical fabrication of nanoscale structures.
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01 Jan 2006
TL;DR: In this paper, the basic theory of heterogeneous nucleation has been studied, including phase equilibrium, formation free energy, equilibrium cluster distribution, and nucleation kinetics, and basic nucleation theorems.
Abstract: Fundamentals of thermodynamics.- Phase equilibrium.- Formation free energy.- Equilibrium cluster distribution.- Nucleation kinetics.- Nucleation theorems.- Basics of heterogeneous nucleation.- Beyond the classical theory.
TL;DR: A theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.
Abstract: The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.