SURFACE RHEOLOGY OF POLYMERIC SOLIDS

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic(SVM)and lateral force microscopic(LFM)measurements.SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene(PS)with sec-butyl and proton-terminated end groups atroom temperature.In the case of the number-average molecular weight,M_(n),less than ca.4.0×10^(4),the surface was in a glass-rubber transition state even though the bulk glass transition temperature,T_(g)was far above room temperature,meaning thatthe surface molecular motion was fairly active compared with that in the bulk.LFM measurements of the,monodisperse PSfilms at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to thesurface mechanical relaxation behavior and also that the surface glass transition temperature,T_(g)^(σ),was depressed incomparison with the bulk one even though the magnitude of M_n was fairly high at 1.40×10~5.The surface molecular motionof monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanningviscoelasticity microscopy(TDSVM).The T_(g)^(σ)s for the PS films with M_n of 4.9×10^(6)to 1.45×10^(6)measured by TDSVMwere smaller than those for the bulk one,with corresponding M_ns,and the T_(g)^(σ)s for M_ns smaller than ca.4.0×10^(4)were lowerthan room temperature(293 K).The active thermal molecular motion at the polymeric solid surface can be interpreted interms of an excess free volume near the surface region induced by the surface localization of chain end groups.In the case ofM_n=ca.5.0×10^(4),the T_(g)^(σ)s for theα,ω-diamino-terminated PS(α,ω-PS(NH_2)_2)andα,ω-dicarboxy-terminated PS(α,ω-PS(COOH)_2)films were higher than that of the PS film.The change of T_(g)^(σ)for the PS film with various chain end groups canbe explained in terms of the depth distribution of chain end groups at the surface region depending on the relativehydrophobicity.

MICROSCOPIC HETEROGENEITY IN VISCOELASTIC PROPERTIES OF MOLECULAR ASSEMBLED SYSTEMS

An important step in understanding molecular assembled systems is to examine the structure and physical properties at various length scales and clarify the correlation between them. However, while the structures of these systems have been extensively studied from nanoscopic to macroscopic scales, their viscoelastic properties have been often limited to bulk rheological measurements. By using optical tweezers and particle tracking, we here show the local viscoelastic properties and their spatial distributions for the following systems： worm-like micelle solution, supramolecular hydrogel and lyotropic liquid crystal, which are formed by self-assembly of amphiphilic molecules in water. We found that all systems studied possessed a spatial heterogeneity in their viscoelastic properties and this was originated from the heterogeneous structures. It is interesting to note that there is the heterogeneity with the characteristic length scale of sub-micrometer or micrometer scale, thereby structures, although the systems are formed by molecules with nanometer size. The findings of these studies should lead to a better understanding of the dynamics of such systems.

Detuning Tolerance of 50 GHz-Spaced 40 Gbit/s-Based DWDM System

Impact of detuning between signal wavelength and MUX/DEMUX filter passband in WDM systems was numerically studied for 50 GHz-spaced 42.7 Gbit/s RZ and CS-RZ signals. RZ signal was found more robust against signal wavelength detuning but not against filter detuning.