Alamgir Karim

Bio: Alamgir Karim is an academic researcher from University of Houston. The author has contributed to research in topics: Polymer blend & Thin film. The author has an hindex of 56, co-authored 302 publications receiving 11546 citations. Previous affiliations of Alamgir Karim include National Institute of Standards and Technology & University of Akron.

A buckling-based metrology for measuring the elastic moduli of polymeric thin films

Abstract: As technology continues towards smaller, thinner and lighter devices, more stringent demands are placed on thin polymer films as diffusion barriers, dielectric coatings, electronic packaging and so on. Therefore, there is a growing need for testing platforms to rapidly determine the mechanical properties of thin polymer films and coatings. We introduce here an elegant, efficient measurement method that yields the elastic moduli of nanoscale polymer films in a rapid and quantitative manner without the need for expensive equipment or material-specific modelling. The technique exploits a buckling instability that occurs in bilayers consisting of a stiff, thin film coated onto a relatively soft, thick substrate. Using the spacing of these highly periodic wrinkles, we calculate the film's elastic modulus by applying well-established buckling mechanics. We successfully apply this new measurement platform to several systems displaying a wide range of thicknessess (nanometre to micrometre) and moduli (MPa to GPa).

Interaction of Gold Nanoparticles with Common Human Blood Proteins

Abstract: In order to better understand the physical basis of the biological activity of nanoparticles (NPs) in nanomedicine applications and under conditions of environmental exposure, we performed an array of photophysical measurements to quantify the interaction of model gold NPs having a wide range of NP diameters with common blood proteins. In particular, absorbance, fluorescence quenching, circular dichroism, dynamic light scattering, and electron microscopy measurements were performed on surface-functionalized water-soluble gold NPs having a diameter range from 5 to 100 nm in the presence of common human blood proteins: albumin, fibrinogen, γ-globulin, histone, and insulin. We find that the gold NPs strongly associate with these essential blood proteins where the binding constant, K, as well as the degree of cooperativity of particle−protein binding (Hill constant, n), depends on particle size and the native protein structure. We also find tentative evidence that the model proteins undergo conformational cha...

Spinodal Dewetting of Thin Polymer Films

Abstract: Dewetting of polystyrene films on a silicon substrate is investigated as a function of film thickness $h$. We observe the nucleation of holes in the early stage of dewetting for relatively thick films $(hg100\AA{})$, as observed previously, but the breakup of thinner films occurs through the growth of uniformly distributed surface undulations (``spinodal dewetting''). The average amplitude $\ensuremath{\delta}h$ of these undulations increases exponentially up to the film rupture point where $\ensuremath{\delta}h$ becomes comparable to $h$, as predicted by a capillary wave instability model.

Phase-Separation-Induced Surface Patterns in Thin Polymer Blend Films

Abstract: Atomic force microscopy (AFM), neutron reflection (NR) and secondary ion mass spectroscopy (SIMS) are used to examine phase separation in symmetrically segregating thin polymer blend films (≤1000 A). Phase separation in the film leads to undulations of the liquid−air interface, provided the film is sufficiently thin to suppress surface-directed spinodal decomposition waves. Flattened droplets are formed at a very late stage of phase separation, and the aspect ratio of these droplets can be rationalized by an interfacial free energy minimization argument.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Thiol–Ene Click Chemistry

Abstract: Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chemistry communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, we review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymerizations resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymerization are all reviewed.