Poly fabrication methods

HoUow-fiber fabrication methods can be divided into two classes (61). The most common is solution spinning, in which a 20—30% polymer solution is extmded and precipitated into a bath of a nonsolvent, generally water. Solution spinning allows fibers with the asymmetric Loeb-Soufirajan stmcture to be made. An alternative technique is melt spinning, in which a hot polymer melt is extmded from an appropriate die and is then cooled and sohdified in air or a quench tank. Melt-spun fibers are usually relatively dense and have lower fluxes than solution-spun fibers, but because the fiber can be stretched after it leaves the die, very fine fibers can be made. Melt spinning can also be used with polymers such as poly(trimethylpentene), which are not soluble in convenient solvents and are difficult to form by wet spinning. 

The poly(ether/amide) thin film composite membrane (PA-100) was developed by Riley et al., and is similar to the NS-101 membranes in structure and fabrication method 101 102). The membrane was prepared by depositing a thin layer of an aqueous solution of the adduct of polyepichlorohydrin with ethylenediamine, in place of an aqueous polyethyleneimine solution on the finely porous surface of a polysulfone support membrane and subsequently contacting the poly(ether/amide) layer with a water immiscible solution of isophthaloyl chloride. Water fluxes of 1400 16001/m2 xday and salt rejection greater than 98% have been attained with a 0.5% sodium chloride feed at an applied pressure of 28 kg/cm2. Limitations of this membrane include its poor chemical stability, temperature limitations, and associated flux decline due to compaction. 

There are a variety of materials that can be used as sacrificial cores. Inorganic sacrificial materials include Si02 and metals such as aluminum, " titanium, and nickel. Polymers such as PI, PMMA, PC, and photoresist have also been used as sacrificial materials. After deposition of the cover film, removal of the sacrificial layer can be achieved by dissolution, etching, or thermal degradation. These removal methods each have benefits and drawbacks selection of the optimal approach is specific to particular combinations of substrate, sacrificial layer, and cover film 73, 3 Recently Whitesides and coworkers " implemented a fabrication method using water-soluble sacrificial cores. Poly(acrylic acid) and dextran proved to be effective sacrificial layers that could be dissolved in water or aqueous NaCl, for making metallic microstructures by nickel electrodeposition. 

Many efforts have been devoted to the microcapsules with tailored structure and the fabrication methods thereof. Examples like double-shell microcapsule of polyurea/polyurethane show improved thermal mechanical property and ethanol resistance, poly(acrylonitrile-divinylbenzene-styrene)/polyamide two-layer microcapsule was prepared to encapsulate water, and self-bursting microcapsules " may have potential application in agricultural field because of its unique release profile. Additionally, monodispersed microcapsules based on miCTofludic processes like SPG (Shirasu... 

Broadhead and Tresco studied the effects of fabrication conditions on the structures and performances of membranes formed from poly(acrylonitrile-vinylchloride) (PAN-PVC) by using the phase inversion process [85]. They reported the relationship of the fine-surface structure of PAN-PVC membranes to the membrane performance and membrane fabrication method. The fine-surface structure of nodular elements and the size of these elements could be altered by changing the precipitation conditions. Membranes were prepared at 22 on 55 mm diameter polished silicon wafers by spinning at 1500 rpm for 20 s with a spin coater [86]. The film was immediately precipitated in one of the four different precipitation media. The first three media consisted of deionized water at 4,22, and 54 °C. These membranes were referred to as Type 1 , Type 2 , and Type 3 , respectively. The fourth medium was a 50/50 mixture of deionized water and N,iV-dimethylformamide (DMF) at 54 °C and coded as Type 4 . Figure 4.53 shows the histograms of the nodule size distributions observed at the skinned surface of the membranes made under four different precipitation conditions. The sizes of these nodular elements became smaller and more uniform with milder precipitation conditions, which supports the theory that nodules are formed through spinodal decomposition under these conditions. In addition, the size of these nodules could be related to water permeability. Hence, water transport occurred through the interstitial spaces where the pores could be situated. 

A similar treatment was used to electrospin poly(vinylidene fluoride] (PVDF]/PPy composites, which were prepared by spinning a nonwoven web from a solution of PVDF and CUCI2.2H2O in dimethylacetamide (DMAc) and then exposing the spun fibers to Py vapors in order to produce the conductive composites. The electrical conductivity of the PPy composites was affected by the fabrication method and oxidant content in the nonwoven web. 

Herein five conducting polymers such as polypyrrole (PPy), polyaniline (PANI), polythiophene (PT), poly(3,4-ethyelenedioxythiophene) (PEDOT) and poly(p-phenylene vinylene) (PPV) are selected for this review. Although other conducting polymers are also noteworthy, 1 do not describe them here because I would hke to concentrate on the fabrication methods and applications of common conducting polymers that are prepared from simple monomers. Molecular structiues of these typical conducting polymers are shown by Table 1. 

Kenaf fibers can be also used for the reinforcement of poly(propyl-ene) (PP) (27). In a study, the optimal fabrication method for such materials was investigated. It turned out that a compression molding process is most promising. A layered sifting of a microfine PP... 

Poly Hi Solidur Plastics India Limited [4] developed products for use on the Indian Railways based on ultra-high molecular weight PE (UHMWPE Hoechst s Hostalen GUR). The base polymer is mixed with patented additives and uses a computer controlled sintering process and sophisticated fabrication methods to produce a material which is claimed to have much higher values for a number of technically important properties such as wear, chemical and water resistance, impact strength and dynamic coefficient of friction. The growth of the market for UHMWPE products is briefly discussed, and the applications targeted by Poly Hi Solidur Plastics are discussed. 

Recent research explored various chemically modified conjugates and derivatives to improve its physico-chemical and biological properties. This modification allows significant applications of chitosan in various disciplines of biomedical research. So far various fabrication methods have been employed for the development of chemically modified chitosan e.g. chitosan-poly(acrylic acid) nanoparticles and acylated chitosan nanoparticles have been recently explored to examine their modifications effect on physicochemical properties and blood compatibility [151, 152], Similarly self-aggregated NPs of cholesterol-modified 0-carboxymethyl chitosan conjugates were fabricated to improve the pharmaceutical and biomedical applications of chitosan [153], Various examples of chitosan and its chemically modified synthetic derivatives are mentioned in Table 3.2. 

The choice of the passive membrane material is critical to the performance of micropump and is often dictated by the type of actuator and the fabrication method selected. For micropumps driven by low frequency and/or low-force actuators, a low-modulus material generally allows the volume displaced by the membrane to be maximized, favorably impacting performance. Commonly used low modulus materials for membranes are elastomers, poly-imide, pyrelene, and polydimethylsiloxane (PDMS), and silicone rubber. However, since the membranes act against... 

Due to the high commercial potential of CP-LEDs, the search for better fabrication methods as well as better materials has also continued aggressively. For example, Fukuda et al. [788] recently studied poly(quinoxaline-5,8-diyl) (P(Qx), structure shown in Fig. 16-27. as a superior electron injection material. A device configuration such as ITO/P(PV)/P(Qx)/Metal was shown to be more efficient than alternative configurations without P(PV) and P(Qx). Fig. 16-27b compares these several configurations schematically, whilst Fig. 16-27c shows representative luminescence characteristics of the first configuration. 

Notably, this fabrication method can also be applied to other polymers, such as PVAc and poly(w-isopropylacrylamide) (PNIPAm). The unusual phase transition behavior of the fabricated MMT-PNIPAm nanocomposites has been reported to be due to the hydrogen bonding between the... 

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