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

High-resolution birefringence investigation on the effect of surface-functionalized CdSe nanoparticles on the phase transitions of a smectic — A liquid crystal

Random copolymers of poly(ethylene oxide) macromonomer with p‐vinylbenzyl end‐functional group (PEOVB) and liquid crystalline monomer, namely 6‐(4‐cyanobiphenyl‐4′‐oxy)hexyl acrylate (COA), were prepared by conventional free radical polymerization. A living anionic polymerization technique was employed for the synthesis of PEO macromonomers bearing p‐vinylbenzyl moiety at one end. The photon transmission method was also applied to study the phase transitions of COA monomer and its random copolymer with PEO. It was found that, for both samples, the nematic‐smectic A transition is continuous, but the critical fluctuation regions do not allow to obtain 3D XY values. Instead, we have obtained the values close to mean field regime. Scaling of thermal hystersis for random copolymer sample near the nematic‐isotropic transition was studied as well. Thermal hysteresis loops were produced under linearly varying temperature. It was shown that the areas of the hysteresis loops scale with the temperature scanning rate...

Synthesis and Liquid Crystalline Behavior of Random Copolymer of Poly(ethylene oxide) Macromonomer and Liquid Crystalline Monomer by the Photon Transmission Technique

Dielectric spectroscopy of liquid crystalline cyanobiphenyl polyacrylates (CBPA6) with six methylene groups in the side chain has been investigated in the frequency range of 30 Hz–13 MHz and in the temperature interval from 100 to 470 K. From the temperature dependence of e'(T), the anomalies corresponding to sequential phase transitions of liquid crystalline mesophases were revealed. The observed α- and δ-relaxation processes were described by the Vogel–Fulcher–Tammann law. It was found that δ-relaxation exhibits a multistage slowing behavior with decreasing temperature. The existence of a reentrant nematic (Nre) phase upper glassy phase shows us the special conditions for glass transition: the enhancement of the degree of cooperativity in mesogenic subsystems due to corrugation effects results in interaction of the side chain modes with a mixture of segmental and normal modes of the backbone, leading to a step-like anomaly of e'(T) at the glass transition.

https://iopscience.iop.org/article/10.1088/0953-8984/20/03/035106/pdf

Dielectric relaxation in a thermotropic side chain liquid crystalline polymer with nematic reentrant phase

Within the entire mesomorphic range, high-precision dielectric anisotropy data with the high-temperature resolution is presented for a highly polar smectic-A liquid crystal 8CB (octylcyanobiphenyl) as well as 8CB nanocomposites doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWCNTs). The temperature variation of the nematic order parameter across both the nematic-isotropic (N-I) and the nematic-smectic-A (N-Sm-A) phase transitions of the neat 8CB and 8CB+MWCNT nanocomposites has then been derived from the dielectric anisotropy data within the framework of the Maier-Meier theory. With the inclusion of MWCNTs, both the N-I and the N-Sm-A transition temperatures have been noted to shift to lower temperatures as compared to the 8CB host. Also, for all 8CB+MWCNT nanocomposites, regardless of the surface functionalization, it has been well documented that the N-I transition is weakly first order, whereas the N-Sm-A transition remains continuous within the experimental resolution. For all investigated samples, the temperature dependence of the nematic order parameter has been shown to be quasitricritical, within the experimental resolution. From the attentive inspection of the dielectric anisotropy data in the vicinity of the N-Sm-A transition, the upper limits for a possible latent heat ΔH_{NA} for the 8CB host and all 8CB+MWCNT composites, for the first time, have been derived. The so-derived ΔH_{NA} values for all investigated samples have also been compared with those extracted from the optical birefringence data, and an excellent consistency has then been noted. The N-Sm-A pretransitional anomaly has been investigated and the effective specific heat capacity exponent α values have been yielded from the power-law analysis of our high-resolution Δɛ(T) data across the N-Sm-A transition for all investigated samples. It has been well documented that the incorporation of MWCNTs to the 8CB host leaves the N-Sm-A transition essentially bulklike. We discussed that, to some extent, the compliance of MWCNTs does not drive the N-Sm-A transition to 3D-XY-like behavior, that is the strength of de Gennes coupling will remain the same for all nanocomposites. This issue can be ascribed to the weaker nature of MWCNT disorder. In this work, for the first time, high-resolution Δɛ(T) data has been shown to be very adequate and offer an easy way to investigate the N-Sm-A transition as compared to calorimetric methods.

High-resolution dielectric anisotropy investigation of carbon nanotube-smectic-A liquid crystal dispersions: An upper limit of the latent heat and the pretransitional anomaly at the nematic-smectic-A transition.

Sevtap Yildiz

Papers

High-resolution birefringence investigation on the effect of surface-functionalized CdSe nanoparticles on the phase transitions of a smectic — A liquid crystal

Synthesis and Liquid Crystalline Behavior of Random Copolymer of Poly(ethylene oxide) Macromonomer and Liquid Crystalline Monomer by the Photon Transmission Technique

Dielectric relaxation in a thermotropic side chain liquid crystalline polymer with nematic reentrant phase

High-resolution dielectric anisotropy investigation of carbon nanotube-smectic-A liquid crystal dispersions: An upper limit of the latent heat and the pretransitional anomaly at the nematic-smectic-A transition.