In a miscible polymer blend the local environment of a monomer of type A will, on average, be rich in A compared to the bulk composition, φ, and similarly for B; this is a direct consequence of chain connectivity. As a result, the local dynamics of the two chains may exhibit different dependences on temperature and overall composition. By assigning a length scale (or volume) to particular dynamic mode, the relevant “self-concentration” φs can be estimated. For example, we associate the Kuhn length of the chain, lK, with the monomeric friction factor, ζ, and thus the composition and temperature dependences of ζ should be influenced by φs calculated for a volume V ∼ lK3. An effective local composition, φeff, can then be calculated from φs and φ. As lower Tg polymers are generally more flexible, the associated φ s is larger, and the local dynamics in the mixture may be quite similar to the pure material. The higher Tg component, on the other hand, may have a smaller φs, and thus its dynamics in the mixture w...

Self-Concentrations and Effective Glass Transition Temperatures in Polymer Blends

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (3 H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

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Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

The small angle neutron scattering experiments were conducted on N‐isopropyl acrylamide (NIPA) gels in D2O and on the corresponding NIPA solutions. The NIPA gels underwent a sharp, but a continuous volume phase transition at 34.6 °C from a swollen state to a shrunken state with increasing temperature. In the case of the gels, an excess scattering due to the presence of crosslinks was observed at low q region (q≤0.02 A−1), where q is the magnitude of the scattering vector. The scattered intensity function for the gel was well described with a combination of Gauss and Lorentz‐type functions, i.e., I(q)=IG(0)exp[−Ξ2q2]+[IL(0)/(1+ξ2q2)] as proposed by Geissler et al. IG(0) and IL(0) are the intensities at q=0 for the contributions of Gaussian and Lorentzian functions, respectively. The Gaussian part results from solidlike inhomogeneity, having a characteristic size of Ξ, which is due to the introduction of crosslinks into the system. The Lorentzian part is originated from the liquid nature of the local concen...

Small angle neutron scattering study on poly(N‐isopropyl acrylamide) gels near their volume‐phase transition temperature

Monte Carlo simulations are presented for a model of a symmetrical polymer mixture on the simple cubic lattice, modeling both polymers A, B by self‐avoiding walks of NA=NB=N steps. If a pair of nearest‐neighbor sites is taken by monomers of the same species, an energy e is won. In the Monte Carlo algorithm local motions of the chains are considered (allowing for 20% vacancies to ensure enough chain mobility) as well as transformations of A chains into B chains and vice versa, since the simulation applies the grand‐canonical ensemble where the chemical potential difference rather than the volume fraction is fixed. The phase diagram, the excess specific heat, and the structure factor in the long‐wavelength limit are obtained for N=4, 8, 16, and 32 using finite L×L×L lattices with L ranging from 8 to 20. Analyzing these results with finite size scaling techniques, both critical exponents and critical amplitudes are estimated. Although the exponents are consistent with those of the three‐dimensional Ising mod...

Critical properties of the Flory–Huggins lattice model of polymer mixtures

Un mixing kinetics and ordering processes of polymer mixtures quenched into thermo-dynamically unstable states are reviewed with particular emphasis on (i) universality in the polymer dynamics in comparison with the dynamics for other systems, such as small molecular fluid mixtures, metallic alloys and inorganic glasses, and (ii) some unique characteristics associated with long-chain molecules (polymer effects, especially the effects resulting from molecular entanglements). The isothermal un mixing behaviors are experimentally studied by real-time analyses of light-scattering from samples subjected to a temperature jump from a single-phase to a two-phase region and are studied from the very early stage to the late stage, in a reduced time scale (τ) of 1 × 10−2 to 2 × 103. Some experimental results are analyzed on the basis of existing theories, and universality and polymer effects are discussed.

Dynamics in spinodal decomposition of polymer mixtures

Influence de la deuteriation du polystyrene dans le melange polystyrene hydrogene/poly(methyl vinyl ether)

Deuteration effects on the miscibility and phase separation kinetics of polymer blends

Cloud points were observed in the blends of deuterated polystyrene (PSD) and hydrogeneous poly (vinyl methyl ether) (PVME) by means of temperature scanning Small Angle Neutron Scattering (SANS) technique. The scattering function in the miscible region can be described by the random phase approximation results calculated by de Gennes. This scattering function can also be expressed in the Ornstein-Zernike form in the small q region. A correlation length and spinodal point can then be determined from this critical fluctuation approach.

Neutron cloud poinds and concentration fluctuations of polymer blends

Resines du diglycidylether du bisphenol A et de diamines lineaires de polyoxyde de propene, gonflees dans l'acetone deuteriee

Hsinjin Yang

Papers

Deuteration effects on the miscibility and phase separation kinetics of polymer blends

Neutron cloud poinds and concentration fluctuations of polymer blends

Epoxy network structure. 4. A neutron scattering study of epoxies swollen in a deuteriated solvent