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RISS 인기검색어
- 검색키워드
- 저자 : Chinedum O. Osuji (검색결과 5 건)
- 무료
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Effect of Final Monomer Deposition Steps on Molecular Layer-by-Layer Polyamide Surface Properties
Tousley, Marissa E.,Shaffer, Devin L.,Lee, Jung-Hyun,Osuji, Chinedum O.,Elimelech, Menachem American Chemical Society 2016 Langmuir Vol.32 No.42
<P>A current challenge to desalination membrane technology is the inability to precisely control the properties of the polyamide selective layer due to the complexity of interfacial polymerization. In this study, we investigate the ability of molecular layer-by-layer (mLbL) assembly, an alternative polyamide fabrication technique, to create poly amide surfaces with tunable chemistry. We explore the influence of terminating monomer, monomer deposition time, monomer size, and the presence of underlying ionizable functional groups on mLbL-derived polyamide surface properties. AFM colloidal probe measurements, contact angle titration, QCM cesium adsorption experiments, and XPS data show that polyamide films terminated with m-phenylenediamine or trimesoyl chloride for 20-30 s are chemically similar. Increasing terminating monomer deposition time or using a smaller, more reactive monomer results in more distinct colloidal-probe adhesive interactions, contact angle titration curves, negative charge densities, and near surface atomic compositions. By optimizing the final monomer deposition steps, both amine rich and carboxyl-rich polyamide surfaces can be fabricated, which has implications for the application of mLbL assembly to membrane-based desalination.</P>
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Continuous and patterned deposition of functional block copolymer thin films using electrospray
Hu, Hanqiong,Toth, Kristof,Kim, Myungwoong,Gopalan, Padma,Osuji, Chinedum O. Cambridge University Press (Materials Research Soc 2015 MRS Communications Vol.5 No.2
<▼1><B>Abstract</B><P/></▼1><▼2><P>We report the use of electrospray to continuously deposit thin films, including patterned films, of a block copolymer (BCP). High substrate temperatures led to vertically oriented cylindrical microdomains at the film surface independent of the solvent composition and deposition rates utilized. Conversely, low substrate temperatures resulted in morphologies that were more sensitive to these parameters, with poorly ordered films of globular structures observed at the lowest temperatures considered. The deposition pattern is defined by spatially varying the electric field at the substrate using an underlying charged grid. These results open up new possibilities for patterned deposition of BCP films with morphological control.</P></▼2>
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Rheology of cellulose nanofibrils in the presence of surfactants
Quennouz, Nawal,Hashmi, Sara M.,Choi, Hong Sung,Kim, Jin Woong,Osuji, Chinedum O. Royal Society of Chemistry 2016 SOFT MATTER Vol.12 No.1
<P>Cellulose nanofibrils (CNFs) present unique opportunities for rheology modification in complex fluids. Here we systematically consider the effect of ionic and non-ionic surfactants on the rheology of dilute CNF suspensions. Neat suspensions are transparent yield-stress fluids which display strong shear thinning and power-law dependence of modulus on concentration, G' similar to c(2.1). Surfactant addition below a critical mass concentration cc produces an increase in the gel modulus with retention of optical clarity. Larger than critical concentrations induce significant fibril aggregation leading to the loss of suspension stability and optical clarity, and to aggregate sedimentation. The critical concentration was the lowest for a cationic surfactant (DTAB), c(c) approximate to 0.08%, while suspension stability was retained for non-ionic surfactants (Pluronic F68, TX100) at concentrations up to 8%. The anionic surfactant SDS led to a loss of stability at c(c) approximate to 1.6% whereas suspension stability was not compromised by anionic SLES up to 8%. Dynamic light scattering data are consistent with a scenario in which gel formation is driven by micelle-nanofibril bridging mediated by associative interactions of ethoxylated surfactant headgroups with the cellulose fibrils. This may explain the strong difference between the properties of SDS and SLES-modified suspensions. These results have implications for the use of CNFs as a rheology modifier in surfactant-containing systems.</P>
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Lee, Yea Ram,Park, Daehwan,Choi, Sang Koo,Kim, Miju,Baek, Heung Soo,Nam, Jin,Chung, Chan Bok,Osuji, Chinedum O.,Kim, Jin Woong American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36
<P>Cellulose fibrils, unique plant-derived semicrystalline nanomaterials with exceptional mechanical properties, have significant potential for rheology modification of complex fluids due to their ability to form a physically associated semiflexible fibrillary network. Here, we report new associative cellulose nanocrystals (ACNCs) with stress-responsive rheological behaviors in an aqueous solution. The surface-mediated living radical polymerization was employed to graft poly(stearyl methacrylate-co-2methacryloxyethyl phosphorylcholine) brushes onto the nanofibrils, and then 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was conducted to produce nanoscale ACNCs in the aqueous solution. The ACNCs displayed interfibril association driven by the hydrophobic interaction that resulted in the formation of a nanofibrillar crystalline gel phase. We observed that the viscosity of the ACNC fluid showed reversible shear thinning and temperature-induced thickening in response to applied shear stress and thermal shock. Moreover, thanks to generation of a mechanically robust nanofibrillar crystalline gel network, the ACNC suspension showed extraordinary stability to changes in salinity and pH. These results highlighted that the interfibril hydrophobic association of ACNCs was vital and played an essential role in regulation of stimulireVonsive sol gel transitions.</P>
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