PMMA matrix

Fig. 26. Relationship between the measured interfacial strength and the (negative) Gibbs free energy of mixing, —for glass beads treated with various silane coupling agents embedded in a PMMA matrix. Error bars correspond to 95% mean confidence intervals.

Figure 4.3 shows the fluorescence SNOM images of single PMMA-Pe chains embedded in the unlabeled PMMA matrix. In the SNOM image, each PMMA-Pe chain was observed as an isolated fluorescent spot. The molecular weight of each chain can be estimated from the integrated fluorescence intensity [19], and Figure 4.3... 

Flocculation studies (6) indicated that the mechanism of steric stabilization operates for the PMMA dispersions. The stability of PMMA dispersions was examined further by redispersion of the particles in cyclohexane at 333 K. Above 307 K, cyclohexane is a good solvent for PS and PDMS, and if the PS-PDMS block copolymer was not firmly anchored, desorption of stabilizer by dissolution should occur at 333 K followed by flocculation of the PMMA dispersion. However, little change in dispersion stability was observed over a period of 60 h. Consequently, we may conclude that the PS blocks are firmly anchored within the hard PMMA matrix. However, the indication from neutron scattering of aggregates of PS(D) blocks in PMMA particles may be explained by the observation that two different polymers are often not very compatible on mixing (10) so that the PS(D) blocks are tending to... 

Among other specific applications of PTs as light-emitting materials, it is necessary to mention microcavity LEDs prepared with PTs 422 and 416 [525,526] and nano-LEDs demonstrated for a device with patterned contact structure, and PT 422 blended in a PMMA matrix that emits from phase-separated nanodomains (50-200 nm) [527,528]. 

An effective thickness of the layer where the fluorescence is observed is assumed to be the depth where the excitation light intensity is 1/e of the initial value. The thickness was calculated to be 1.4 im from an absorption coefficient of the film at 295 nm (excitation wavelength). Therefore, the observed fluorescence spectral change is due to that of aggregate states of EPy in the depth region of 1.4 fin from the ablated surface. Actually, it is well known in a PMMA matrix that the excimer band is due to the ground state dimer of the dopant (23). 

IL6 An article related to acrylic bone cements [Abboud, M. et al PMMA-based composite materials with reactive ceramic fillers IV. Radiopacifying particles embedded in PMMA beads for acrylic bone cements, J. Biomed. Mater. Res., 53(6), 728 (2000)] provides the following information on the PMMA matrix used in these cements M, = 295,000 My,/Mn = 2.2. Calculate the number average degree of polymerization for the PMMA used in this study. 

The effect of MDR is experimentally observed in the steady state fluorescence spectra and lifetimes of 9AAHH in single microspheres. From this study, we have determined the femtosecond dephasing time of 9AAHH in PMMA matrix at room temperature. The dephasing time of 9AAHH in PMMA is determined to be 22 fs. 

Fig. 2.29 (a) TEM from a PS-PEB-PMMA triblock with M = 238kgmol l,/pS = 0.47, /peb = 0.075 and /pmma = 0.455. The PS cylinders appear dark and the PMMA matrix is light. The arrow indicates a region where a cross-section of PEB rings (dark) can be seen, (b) Schematic of the morphology (Auschra and Stadler 1993). 

The resulting PE-fr-PMMA was purified by soxhlet extraction with THF and characterized by NMR, DSC, and TEM micrography (Table 1). The TEM of the obtained PE-fr-PMMA revealed unique morphological features which depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50-100 nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix (Fig. 12). Moreover, the PE-b-PMMA block copolymers effectively compatibilized homo-PE and homo-PMMA at a nanometer level (Fig. 13). 

Shang et al. (61) used microemulsion polymerization to synthesize MWCNT-PMMA composites for gas sensor applications. Better dispersion, enhanced electrical conductivity and better sensor response was observed for in-situ fabricated composites compared to composites prepared by solution mixing. Ma et al. (62) performed in-situ polymerization of MWCNT-PMMA composites in the presence of an AC electric field to study dispersion and alignment of MWCNT in PMMA matrix induced by the electric field. Experimental evidences from in-situ optical microscopy, Raman spectroscopy, SEM and electrical conductivity showed that both dispersion and alignment qualities were significantly enhanced for oxidized MWCNT compared to pristine MWCNT. 

The product of the innovated polymerization procedure described above shows a uniform size distribution of spherical particles, with spheres size of 8 pm, contrary to polydispersed MWCNT/PMMA particles 1—12 pm in diameter. The polydispersity may originate from the presence of MWCNT particles (48), and the size of final MWCNT/PMMA spheres depends on MWCNT concentration and size and also on the level of MWCNT aggregation and the number of individual MWCNTs involved in the formation of composite particles. The presence of nanotubes in PMMA/MWCNT composites was confirmed by SEM analysis, which identified a large amount of MWCNTs at the surface of the composite spheres. Some of them are just adhered on PMMA spheres surface but others come into bulk of PMMA matrix. It was also confirmed by TEM analysis that nanotubes are well embedded in the surface of PMMA particles and even more, they are present inside individual PMMA/MWCNT particles. 

Electrorheological phenomenon is demonstrated in Figure 8.13 on optical microscope images of two different types of CNT microspheres. Both are based on PMMA matrix but in the first case the particles were prepared by in-situ suspension polymerization in presence of MWCNT (570 and in the second by MWCNT adsorption on separately prepared PMMA microspheres (20). Particles were dispersed in silicon oil and placed between two parallel electrodes. Figure 8.13(a) represents the state without and Figure 8.13(b) with applied electric field. In the figure, typical ER fibril structures can be observed for both principal materials when external electric field is applied the dispersed PMMA/MWCNT microspheres form chain structures. 

When seeking a polymer material for a CNT-based strain gauge, ductility and ease of processing are the key requirements. For that reason, polymethyl methacrylate (PMMA) and polyethylene (PE) are two candidate materials. Studies on the electrical conductivities of CNT-PMMA composites reported minimum percolation thresholds ranging from 0.084 to 1.3 wt% which depend on the type of CNT (SWNT or MWNT) and the dispersion technique. Such values are much lower than percolation thresholds reported for CNT-PE which rise up to 15 wt% (38). As a consequence, much higher conductivity values were reported for CNT-PMMA composites. For this reason, a PMMA matrix will be considered for the current... 

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