Microgel diameter

Pich and coworkers synthesized microgels by free-radical co-polymerization of vinyl caprolactam and acetoacetoxyethyl methacrylate (AAEM) in the presence of methoxy-capped PEGMA macromonomers [88], It has been reported that variation of the amount of PEG macromonomer or the length of the PEG chain provides effective control of the microgel diameter in the range 60-220nm (Fig. 6). 

FIGURE 62 The dependence of reaction rate constant on microgels diameter 2R for system EPS-l/DDM. 

As it is known [81], in nanochemistry there are two fundamental notions -nanoparticle and nanoreactor the first characterizes dimensional parameter while the second one defines nanoobject function. Thus, iron clnster loses almost completely its specific properties (ionization energy, magnetism) and approaches to metallic iron with an atoms mtmber in cluster n = 15. Atn> 15 it remains nanoobject in dimensional sense, bnt loses nanoreactor qualities, for which properties become a size function. In Fig. 44, the dependence of cnring rate constant k on microgels diameter 2R, which has a very specific form, is adduced. 

Figure 8.7 Encapsulation efficiency at va -ing cell concentration and microgel diameter. Experimental (black) and theoretical (gray) fractions of microgels encapsulating at least one cell are plotted for 70 and 110 Jim...

The particle diameter of the GPC column stationary phase plays a role not just in determining the resolution of the column, but also in determining how well the column elutes insolubles or microgels that may be present. It is usually advisable to avoid the injection of insolubles or microgels that might block the frits or interstices of any GPC column, but in some instances the analysis of these materials by GPC is possible and even desirable. 

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

The supports are soluble microgels and pore diameter cannot be measured. 

Microemulsions are a convenient medium for preparing microgels in high yields and rather uniform size distribution. The name for these special emulsions was introduced by Schulman et al. [48] for transparent systems containing oil, water and surfactants, although no precise and commonly accepted definitions exist. In general a microemulsion may be considered as a thermodynamically stable colloidal solution in which the disperse phase has diameters between about 5 to lOOnm. 

By emulsion copolymerization (ECP) of self-emulsifying unsaturated polyesters (EUP) and bifunctional monomers, such as styrene (S), microgels may be prepared which have a rather uniform diameter [109]. This uniformity of size is due to a special mechanism of particle formation involved in using EUP as comonomers. 

As the EUP is an emulsifier, an increase of the EUP/comonomer ratio not only causes an increase of the number of micelles and microemulsion droplets respectively but also of the number of microgels and, correspondingly, a decrease of their molar mass [110,126] and their diameter [127]... 

Because the presence of an electrolyte increases the dimensions of micelles and microemulsion droplets [115], it may be expected that in presence of ions the size of microgels is also increased. This expectation could be confirmed external electrolyte increases Mw (Fig. 21) as well as dz and [r ] (Fig. 22) up to the limit of the emulsion stability. Therefore, the addition of an external electrolyte to the reaction mixture for the ECP of EUP and comonomers is a means to vary the molar mass, the diameter and the intrinsic viscosity of microgels from EUP and comonomers deliberately. 

Fig. 57. Diameters of microgels prepared with different emulsifier concentrations (SDS). Composition (mol %) NjN -tetramethylenebismethacrylamide (10%),N-n-hexylmethacrylamide, propenic acid amide-N-(4-methyl-2-butyl-l,3 dioxolane (50%)...

A microgel of a dz = 76 nm which is suitable for coupling with proteins, can be prepared by emulsion terpolymerization of NjAT -tetramethylene bisacrylamide, n-hexylmethacrylamide and propene acid amide-N-(4-methyl-2-butyl-1,3-diox-olane) [291 ]. The diameter of these microgels may be varied by the concentration of the emulsifier (Fig. 57) and is rather uniform. As the CMC of this system is about 2.5 X10"3 mol SDS/1, it may be assumed that below this value the copolymerization essentially takes place in the monomer droplets, whereas at higher concentrations of SDS preferentially the monomers in micelles are polymerized. 

For small microgels, like crosslinked particles of a microemulsion (diameter below 102 nm), the definition of the gel point is no longer clear. For instance, a... 

Particle of gel of any shape with an equivalent diameter of approximately 0.1 to 100 pm. Modified from [2]. The definition proposed here is recommended for its precision and because it distinguishes between a microgel and a nanogel. 

A new synthetic protocol for the synthesis of large diameter (2.5-5pm), temperature-, and pH-responsive microgels via aqueous surfactant-free radical... 

Li et al. [100] synthesized core-shell microgels with temperature-sensitive PNIPAAm core and pH-sensitive poly(4-vinylpyridine) (P4VP) shell. Narrowly distributed microgel particles with core diameter of 95 nm and shell thickness of approximately 30 nm were obtained. 

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