Polydiacetylene fiber

Fig. 20. Stress distribution along polydiacetylene fiber in model composite. Calculated...

Fig. 21. Kinks measured for fibers in model composites, (a) The change in the backbone stretching vibration as a function of temperature for polydiacetylene fiber in model composite. — — Tc = 20°C — — Tc = 60°C — — = 100°C. (b) Polydiacetylene fiber...

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

Reppy MA, Pindzola BA (2006) Polydiacetylene liposomes attached to glass fibers for bioassays. Mater Res Soc Symp Proc 942(0942) W13-10... 

Figure 12.7 Photographs of electrospun fiber mats embedded with 1 (a) before and (b) after 254-nm UV irradiation (1 mW/cm ) for 3 min. (c) Scanning electron microscopy image of the microfibers containing polymerized 1. (c) Photographs of the polydiacetylene-embedded electrospun fiber mats prepared with various diacetylene monomers after exposure to organic solvent. Reprinted fi om Yoon et al. (2007). Copyright 2007 American Chemical Society. (See color insert.)...

Unfortunately, apart from one or two polymers that can be polymerized in the solid state from single crystals of monomers (e.g., polydiacetylenes), polymers cannot be obtained as single crystals. Most often, patterns are obtained from oriented fibers and... 

Different attempts to lock-in the long-range orientational order of the mesophases of the copper(II) carboxylates have been reported. One of them consisted of replacing the alkanoic acid moiety with a diacetylenic acid, namely, pentacosa-10,12-diynoic acid, to lead to a new mesogenic material which can then be polymerized. The copper complexes formed exhibited a mesophase with a lamello-columnar order, which has been processed into highly ordered crystalline fibers which were polymerized by UV radiation without disruption of the mesomorphic order. The combination of fiber morphology, order, and the presence of oriented polydiacetylene networks suggest that these systems could be of some interest as optically non-linear media. 

Recently, liu et al. [33, 34] reported an absolute asymmetric transformation when the achiral monomer 10,12-tricosadiynoic acid was deposited on an aqueous solution containing Cu + ions. The monolayer was then transferred to a solid support as a Langmuir-Blodgett film, followed by photo-polymerization to yield a stable homochiral polydiacetylene as helical fibers. 

Recent results on the fracture behaviour of advanced fibers and model composite materials (microcoiposites) are presented. The fiber data utilized are strength results for polydiacetylene vdiiskers and Kevlar 149 fibres. The probabilistic approach adopted for the effect of fibre... 

Raman spectroscopy has been applied to determine the stiffness (modulus) of CNCs and stress-transfer in CNCs-reinforced composites or biocomposites where reinforcing phase is too small to be characterized by using standard mechanical techniques. This technique involves the measurement of deformation (a shift in the carbonyl (C-O) mode of the cellulose chain) [96], Originally these shifts of Raman bands were reported for single crystals of polydiacetylene [97] and composites [98] followed by shifts reported for stressed regenerated cellulose fibers [99]. The Raman bands shift is the indication of molecular deformation and determine the extent of stress-transfer between reinforcing CNCs and matrix. The intensity of Raman band measures the orientation distribution of the nanocrystals in composites [96]. Recently, some researchers measured the stress-transfer behavior in microfibrillated cellulose-reinforced polylactic acid and cellulose nanowhiskers-reinforced epoxy-resin composites [96,100]. 

The per chain modulus of this pol3nner is about equal to that of diamond in the [110] direction. A polyethylene fiber with the same per chain mechanical properties would have an ultimate tensile strength in excess of one million psi. The theoretical modulus calculated for a defect free polydiacetylene chain using a spectroscopic force field is within 10% of the observed modulus. This contrasts with the case for conventional polymers, where the bulk tensile modulus is typically much less than 50% of the theoretical (spectroscopic) modulus. 

The approach that was adopted [66-69] was to prepare a series of urethane-diacetylene copolymers in which polydiacetylene units are incorporated into segmented copolyurethanes. It was shown in Section 8.1.1 that large strain-induced Raman band shifts can be obtained during the deformation of polydiacetylene single crystal fibers [8-12]. In fact, it is found that the largest shift measured so far (—20cm"V% strain) is for the C=C triple bond stretching band of polydiacetylenes (Table 8.1). 

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