Polymer shell thickness

Figure la shows that the maximal extinction increases with increasing adsorbed polymer shell thickness and shell refractive index. All curves have a maximum for gold core diameters 60-80 nm. This maximum is closely related to the optimizatiou problems discussed in Refs. [12, 17]. For small particles, the shift of extinction plasmon resonance can be described by a universal dependence [12, 51]. In the first approximatiorr, the optical properties of bioconjugates are well explained by a simple two-layer electrostatic model (previous analysis [43] contairrs some inacctrracies, see Ref [12]). We shall consider the extinction spectra only. For small conjugates, the extinction is determined by the absorption efficiency... 

Table 1. Comparison of the statistically averaged optical parameters A, with those calculated with both orientation and statistical averaging, A), (/j ). Calculations for ballistic clusters built from gold particles with diameters rf = 15 and 30 nm, polymer shell thickness and refractive index s = 2.5 nm and n = A, respectively. All data are averaged over 100 independent cluster configurations.

The flow behavior of the polymer preferentially influences the uniform shell thickness and is related directly to the molecular structure of the modifying comonomer. Modifications of PET, particularly with CHDM, improve the flow behavior during injection molding and significantly reduce the melting point of the polymer. The decreased melting point of the copolymer allows reduced processing temperatures and therefore correlates with a reduced formation of unwanted A A at shortened cycle times. 

The thickness of the imprinted polymer shell can be also tuned in the range 10—40 nm by changing the relative amounts of functionalised silica nanoparticles and polymer shell precursors. The resulting core-shell particles exhibit enhanced capacity of rebinding the TNT template over 2,4-dinitrotoluene in comparison to particles prepared by precipitation polymerisation. Nevertheless, this strategy, although leading to impressive results, cannot be easily applied to other templates and monomers. 

Preformed polymers can also be employed to prepare imprinted core-shell particles [143]. The group of Chang recently prepared a poly(amic acid) bearing oestrone as a template molecule covalently bound to the polymer through a urethane linker (see Fig. 2). A layer of this polymer was subsequently deposited on silica particles (10 pm diameter) prefunctionalised with amino groups at their surface. Thermal imidisation of the polymer yielded finally a polyimide shell (thickness about 100 nm) on the silica particles. Subsequent template removal yielded the imprinted cavities, which exhibited selective rebinding of oestrone in HPLC experiments. 

CPO-coated magnetic nanoparticles with iron oxide core and polymer shell The thick polymer shell increased the stability of the nanobiocatalyst, giving no loss of activity after recycling 11 times [24]... 

Berkland, C. Pollauf, E. Pack, D.W. Kim, K.K. Uniform double-walled polymer microspheres of controllable shell thickness. J. Controlled Release 2004, 96, 101-111. 

Silica microspheres ( 3 /tm) with initiating moiety (S-8) induced the copper-catalyzed radical polymerization of benzyl methacrylate to form polymer layers on the surface.459 The thickness of polymer shell can be increased to 550—600 nm, where the Mn and MWDs of the arm polymers were 26500 and 1.26, respectively. Removal of the core silica by chemical etching gave uniform hollow polymer microspheres. 

We argue that the above features of star dynamics are generic for soft systems of the core-shell type for which stars serve as prototype. Support for this comes from the dynamic light scattering (DLS) investigation of large block copolymer micelles, where all three relaxation modes, i.e., cooperative, structural and selfdiffusion are observed [188]. In particular, the star model discussed above applies to core-shell particles with a small spherical core relative to the chain (shell) dimensions. For a surface number density a = f / (47i r ) the polymer layer thickness under good solvent conditions is L ... 

Moreover, based on stability relations in architecture it can be proven that the critical fragility of a hollow spherical body depends on the modulus of elasticity of the shell material (a physical constant determined by the nature and molecular weight of the polymer used) and the quotient of shell thickness over size. This means that... 

It is now straightforward (see also Part V, Chapter 6) to fill the capsule not only with air, but a dmg substance too, and to use an ultrasound pulse to trigger the release from outside the body at a defined place and time by bursting the bubble. Utilizing nanotechnological concepts of polymer, colloid and interface science we have established a novel process to manufacture gas-filled microcapsules. On demand, gas filling, elasticity, shell thickness and overall size can be tailored independently. 

Using the so-called two-step process [15, 16], polymer nanoparticles are first synthesized via emulsion polymerization. The size of the resulting nanoparticles can be tuned by a simple process parameter and covers a range of about 30-400 nm. In a second step these nanoparticles are used to coat microbubbles in a controlled bubble formation process. The nanoparticles migrate to the surface of the bubbles (this is related to the interface activity of hydrophobic nanoparticles in general) and build a monolayer around the bubbles. Consequently, the size of the nanoparticles determines the shell thickness of the final microcapsules. Additionally, a carefully chosen nanoparticle concentration regime results in a certain microcapsule size distribution. In principle, particle sizes in the range of 0.5-10 jum can be adjusted and the microcapsule size distributions are ex-... 

With the objective to inve.stigate the dependence of carrier transport on the interchain separation. Riihe et al [252,253] have synthesized doped (C104 ,PF5 ) poly(3,4-cycloalkylpyrrole)s having 3, 4, 5 or 10 methylene groups in the alkyl loop. These polymers arc also amorphous. Because of the interring torsions, the alkyl substituents are expected to form a cylindrical shell around the chain. The thickness of the shell has been estimated from single-crystal x-ray data of the monomers. The conductivity decreases w ith an increase of the shell thickness. This indicates the importance of interchain hopping for this property. 

Polymer adsorption on gold nanoparticles results in two effects (1) it increases the extinction and scattering maxima and (2) it shifts the resonance to the red part of spectrum. Detailed calculations for the gold-core diameters <7 = 10-160 nm, the shell thickness 5=0-10 nm, and the shell refractive indices = 1.4 and = 1.5 can be fotmd elsewhere [12], Here we provide only two examples that illustrate the effect of polymer adsorption on the value of the extinction maximum (Fig. la) and on the extinction peak position (Fig. lb). 

In highly interactive polymer-particle systems, solidlike yield behavior can be observed even at temperatures above the glass transition temperature of the polymer [54]. Polymer molecules can adopt stretched configurations that allow them to adsorb to the surfaces of many particles. Relative motion between polymer chains is retarded by immobilization due to polymer confinement between nanoparticle surfaces. The equilibrium thickness of the immobilized polymer layer is of the order of the radius of gyration of the molecule. Eiller particles can be regarded as hard cores surrounded by immobilized polymer shells of comparable size. 

Bagaria HG, Kadali SB, Wong MS (2009) Shell thickness control of nanoparticle/polymer composite microcapsules (unpublished)... 

Results have been reported on the preparation of monoparticulate films composed of M—Si02 particles. Self-assembly tested on silicon wafers (see Figure 51.12) yielded much better packed films in the presence of a cationic polymer, such as polydimethyldiallyl-ammonium bromide [156] while in any case the films obtained are rather disordered. It is important however that packed films can be obtained from particles with varying particle sizes (shell thicknesses). This shows that intercorrespacing can indeed be tailored through the control of silica shell thickness. The acquisition of optical measurements as a function of shell thickness has been reported [156]. 

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