Polymer bead necklaces

Besides the synthesis of bulk polymers, microreactor technology is also used for more specialized polymerization applications such as the formation of polymer membranes or particles [119, 141-146] Bouqey et al. [142] synthesized monodisperse and size-controlled polymer particles from emulsions polymerization under UV irradiation in a microfluidic system. By incorporating a functional comonomer, polymer microparticles bearing reactive groups on their surface were obtained, which could be linked together to form polymer beads necklaces. The ability to confine and position the boundary between immiscible liquids inside microchannels was utilized by Beebe and coworkers [145] and Kitamori and coworkers [146] for the fabrication of semipermeable polyamide membranes in a microfluidic chip via interfacial polycondensation. 

Figure 22.29 Different types of accessible polymer beads necklaces (a) plain, (b) alternated and (c) block polymer bead necklaces [38],...

This work demonstrates that the use of microfluidic devices allows the synthesis of totally new polymer materials such as polymer bead necklaces, with a large range of morphologies and properties. 

Incorporation of monomers with similar characteristics to the hydrophobic tails of the surfactants involved (typically alkane chains of DODAB and DMPC) tends to suppress phase separation somewhat, and results in either multi-polymer bead aggregates (e.g., necklaces) or parachutes containing an elliptical rather than a spherical latex bead. Copolymerization of butyl methacrylate with ethylene glycol dimethacrylate in DODAB vesicles resulted in polymer necklaces where the polymer beads appear randomly dispersed in the vesicle bilayer [15] in contrast to the polymer shells observed by Hotz and Meier [10] for the same reaction in DODAC vesicles. Similarly, polymerization of octadecylacry-late, another straight-chain monomer, in DODAB vesicles produced parachutes with extremely elHpsoidal polymer beads in contrast to the rather spherical beads observed commonly for the polymerization of aromatic monomers such as styrene in DODAB [12]. Presumably these differences are caused by an increased compatibility between the surfactant bilayer and the monomer chosen. 

Explanation of Property (viii ) of the PVME component in the 25% PVME blend with PS has been offered near the end of the section where these properties are made known. There we have mentioned that this property is shared by some neat glass-formers (Ngai, 2011) including a bead-necklace model for polymer (Bedrov and Smith, 2011) and mixtures of van der Waals liquids (Mierzwa et al., 2008 Kessairiet al., 2008), and the explanation of it readily follows from the co-invariance of r , tjg, and n to changes of pressure and temperature at either constant Tq, or constant tjg, found by experiments and computer simulations. The explanation also follows from the CM equation when combined with the relation, tjg tq, found experimentally valid for many glass-formers between the JG /3-relaxation time and the primitive relaxation time, to, of the CM. 

The units (or beads) of the isomorphic ring polymer (or necklace) correspond to the possible positions of the single quantal electron. 

The focus of this chapter is on an intermediate class of models, a picture of which is shown in Fig. 1. The polymer molecule is a string of beads that interact via simple site-site interaction potentials. The simplest model is the freely jointed hard-sphere chain model where each molecule consists of a pearl necklace of tangent hard spheres of diameter a. There are no additional bending or torsional potentials. The next level of complexity is when a stiffness is introduced that is a function of the bond angle. In the semiflexible chain model, each molecule consists of a string of hard spheres with an additional bending potential, EB = kBTe( 1 + cos 0), where kB is Boltzmann s constant, T is... 

A polymer molecule dissolved in a solvent can be envisioned as a necklace comprising spherical beads connected by a string [23]. The polymer molecules are separated and only interact through the solvent. The Stokes-Einstein equation for the diffnsion coefficient of the polymer can be used for a Flory theta solvent. The root-mean-sqnare... 

Harada et al. reported a molecular abacus (Figure 26) based on a molecular necklace of a-CD threading onto PEG chains." The a-CD beads can be manipulated along a polymer chain by means of acid/base stimulation, which can... 

For the number of charged monomers on the chain fN above the critical value (fN)cnt, the polyelectrolyte chain first forms a dumbbell (see Figure 6 (b)). For larger values of the net charge on the polyelectrolyte chain, the polymer forms a necklace with three beads connected by two strings (see Figure 6(c)). 

Polyelectrolyte chains in a poor solvent for the polymer backbone adopt neddace-like conformations. There are three different length scales in the necklace globule the length of the string the bead size Db, and the thermal blob size fx determining the length scale of density fluctuations inside beads. Thus, all three different length scales will determine the properties of semidilute polyelectrolyte solutions in a poor solvent for the polymer backbone. 

The SANS spectra measured in dilute solutions of water-acetone mixtures of poly(methacryloylethyltrimethylammo-nium methyl sulfate) can be analyzed using the necklace model of polyelectrolyte chains. According to the results of these experiments, each polyelectrolyte chain consists of a sequence of dense beads connected by regions of loose polymer. The radius of these dense beads is about 28 run. Each molecule has about 3-4 dense beads with the volume fraction of polymer inside these globular sections dose to 8%. 

For the effective temperature r (f/M), the correlation length f becomes on the order of the size of a bead Db at polymer concentration cb z. At higher polymer concentrations, the system crosses over into the concentrated polyelectrolyte solution (regime IV). However, if the value of the parameter [r[is larger than (f/ ) the system will phase separate into a concentrated polymer solution and a solution of necklaces. The left boundary of the two-phase region is... 

Thus, the polymer volume fraction in the concentrated phase at the two-phase boundary is the same as inside beads of the necklace globule in the dilute phase. Two lines given by eqns [186] and [187] intersect at and ra -[f ... 

Several coarse-grained geometrical models other than the skeletal chain model are being used to predict how various physical quantities depend on the chain length, the polymer concentration, and so forth, and to perform computer simulations. Figure 1.6 illustrates a bead-stick model (a), a bead-spring model (b), and a pearl-necklace model (c). 

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