Data Reduction And Error Analysis For The Physical Sciences

Telechelic polymers by living and controlled/living polymerization methods

In this work, the classical theory of polymer/polyelectrolyte gel swelling is reviewed. This formalism is easy to understand and has been widely applied to gels and microgel particles. Nevertheless, its limitations and obscure aspects should be known before use. The case of temperature-sensitive gels is discussed in some detail because it deserves particular clarification. The application to experimental swelling data (of both gels and microgels) is also reviewed. In this way, strengths and weaknesses of this approach can be elucidated. Moreover, other formalisms are also outlined. Many of them are inspired by the classical one. Their improvements are briefly commented in this case. Others are based on different grounds.

Gel swelling theories: the classical formalism and recent approaches

Adjusting the acrylamide monomer and cross-linker content in polyacrylamide gels controls the hydrogel stiffness, yet the reported elastic modulus for the same formulations varies widely and these discrepancies are frequently attributed to different measurement methods. Few studies exist that examine stiffness trends across monomer and cross-linker concentrations using the same characterization platform. In this work, we use Atomic Force Microscopy and analyze force–distance curves to derive the elastic modulus of polyacrylamide hydrogels. We find that gel elastic modulus increases with increasing cross-link concentration until an inflection point, after which gel stiffness decreases with increasing cross-linking. This behavior arises because of the formation of highly cross-linked clusters, which add inhomogeneity and heterogeneity to the network structure, causing the global network to soften even under high cross-linking conditions. We identify these inflection points for three different total polymer ...

Tuning the Range of Polyacrylamide Gel Stiffness for Mechanobiology Applications

W H de Jeu 1980 New York: Gordon and Breach ix + 133 pp price $32 It is to be regretted that the practice is growing, even among those knowledgeable in the field, of writing about liquid crystals as though a single type existed and the two processes for their formation produced similar molecular distributions. The distinction between thermotropic and lyotropic liquid crystals is not made in the title of this book.

http://iopscience.iop.org/article/10.1088/0031-9112/32/7/042/pdf

Physical Properties of Liquid Crystalline Materials

We report high-sensitivity and high-temperature resolution experimental data for the temperature dependence of the optical birefringence of a nonpolar monolayer smectogen 4-butyloxyphenyl-4'-decyloxybenzoate (10[over ¯].O.4[over ¯]) liquid crystal by using a rotating-analyzer technique. The birefringence data cover nematic and smectic-A phases of the 10[over ¯].O.4[over ¯] compound. The birefringence data are used to probe the temperature behavior of the nematic order parameter S(T) in the vicinity of both the nematic-isotropic (N-I) and the nematic-smectic-A (N-SmA) transitions. For the N-I transition, from the data sufficiently far away from the smectic-A phase, the average value of the critical exponent β describing the limiting behavior of S(T) is found to be 0.2507±0.0010, which is in accordance with the so-called tricritical hypothesis, which predicts β=0.25 and excludes higher theoretical values. The critical behavior of S(T) at the N-I transition is discussed in detail by comparing our results with the latest reports in the literature and we conclude that by comparing with the previously reported results, the isotropic internal field assumption by the Vuks-Chandrasekhar-Madhusudana model is adequate to extract the critical behavior of S(T) from the optical birefringence data. We observe that there is no discontinuous behavior in the optical birefringence, signaling the second-order nature of the N-SmA transition. The effect of the coupling between the nematic and smectic-A order parameters on the optical birefringence near the N-SmA transition is also discussed. In a temperature range of about 4K above and below the N-SmA transition, the pretransitional evidence for the N-SmA coupling have been detected. From the analysis of the optical birefringence data above and below the N-SmA transition by means of various fitting expressions we test the validity of the scaling relation λ=1-α between the critical exponent λ describing the limiting behavior of the nematic order parameter and the specific heat capacity exponent α. We then show that the temperature derivative of the nematic order parameter S(T) near T(NA) exhibits the same power-law divergence as the specific heat capacity with an effective critical exponent of 0.2303±0.0035.

Critical behavior of a nonpolar smectogen from high-resolution birefringence measurements.

We report optical birefringence data by two different methods with high temperature resolution for octylcyanobiphenyl (8CB) near the smectic-A to nematic (Sm-A-N) phase transition temperature T(AN). Within the resolution of our experiments, we find that the Sm-A-N phase transition is continuous. For a possible discontinuity in the orientational order parameter S(T) at T(AN), we arrive at an upper limit of 0.0002, which is substantially smaller than other estimates in literature, but consistent with the value of 0.00008 derived from the upper limit of the latent heat from high-resolution adiabatic scanning calorimetry (ASC), which is itself consistent with the Halperin-Lubensky-Ma theory. The temperature derivative of the order parameter exhibits a power law divergence with a critical exponent that is consistent with the value α = 0.31 ± 0.03 for the specific heat capacity obtained by ASC.

High-resolution birefringence investigation of octylcyanobiphenyl (8CB): an upper bound on the discontinuity at the smectic-A to nematic phase transition.

The effect of -COOH functionalized carbon nanotube doping on electro-optical, thermo-optical and elastic properties of a highly polar smectic liquid crystal

The effect of surface “aging” on thermotropic properties of polymorphic mesogen, 4-butoxyphenylester of 4-decyloxybenzoic acid (BPEDBA) which exhibits the smectic G, smectic C, smectic A, and nematic mesophases has been investigated. Temperatures of direct and reverse phase transitions and temperature widths of the heterophase regions have been determined with high accuracy. The shift of the phase transition temperatures and change of the temperature widths of the heterophase regions under the influence of surface “aging” have been reported.

Sevtap Yildiz

Papers

Critical behavior of a nonpolar smectogen from high-resolution birefringence measurements.

High-resolution birefringence investigation of octylcyanobiphenyl (8CB): an upper bound on the discontinuity at the smectic-A to nematic phase transition.

The effect of -COOH functionalized carbon nanotube doping on electro-optical, thermo-optical and elastic properties of a highly polar smectic liquid crystal

Change of thermotropic properties in liquid crystal with multiple phase transitions: Surface “aging” effect

Temperature-dependent electro-optical and elastic properties of carbon nanotube doped polar smectogen octylcyanobiphenyl