Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Above a critical size, Co nanoparticles aggregate because of magnetic dipole-dipole interaction into chains. Reported in this paper is the coating of such chains by an AB diblock copolymer in a block-selective solvent for the A block. Also reported is the cross-linking of the deposited or anchored B block of the diblock copolymer to lock in the coating and thus the dipolar chain structure. The Co nanoparticles used were prepared from the high-temperature decomposition of Co(2)(CO)(8) using poly(2-cinnamoyloxyethyl methacrylate)-block-poly(acrylic acid) or PCEMA-b-PAA as surfactant. To coat the dipolar chains, the particles and diblock copolymer poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate), PtBA-b-PCEMA, were dispersed in a good solvent for PCEMA and PtBA. Methanol, a precipitant for PCEMA and a good solvent for PtBA, was then added. This induced the collapsing of the PCEMA blocks and the deposition of the PCEMA block of PtBA-b-PCEMA onto the surface of PCEMA-b-PAA-coated Co nanoparticle chains. The dipolar chains remained colloidally stable in solution for steric stabilization provided by PtBA. The coating was cured by photocrosslinking the PCEMA layer. Such "permanent" and solvent-dispersible Co dipolar chains are novel and may have interesting applications.
ACS Nano 2009 Jan 27
PMID:Coating and structural locking of dipolar chains of cobalt nanoparticles. 1920 63

Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.
ACS Nano 2008 Sep 23
PMID:Reversible clustering of pH- and temperature-responsive Janus magnetic nanoparticles. 1920 18

We present the integration of amphiphilic block copolymer micelles as nanometer-sized vehicles for hydrophobic drugs within layer-by-layer (LbL) films using alternating hydrogen bond interactions as the driving force for assembly for the first time, thus enabling the incorporation of drugs and pH-sensitive release. The film was constructed based on the hydrogen bonding between poly(acrylic acid) (PAA) as an H-bond donor and biodegradable poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) micelles as the H-bond acceptor when assembled under acidic conditions. By taking advantage of the weak interactions of the hydrogen-bonded film on hydrophobic surfaces, it is possible to generate flexible free-standing films of these materials. A free-standing micelle LbL film of (PEO-b-PCL/PAA)60 with a thickness of 3.1 microm was isolated, allowing further characterization of the bulk film properties, including morphology and phase transitions, using transmission electron microscopy and differential scanning calorimetry. Because of the sensitive nature of the hydrogen bonding employed to build the multilayers, the film can be rapidly deconstructed to release micelles upon exposure to physiological conditions. However, we could also successfully control the rate of film deconstruction by cross-linking carboxylic acid groups in PAA through thermally induced anhydride linkages, which retard the drug release to the surrounding medium to enable sustained release over multiple days. To demonstrate efficacy in delivering active therapeutics, in vitro Kirby-Bauer assays against Staphylococcus aureus were used to illustrate that the drug-loaded micelle LbL film can release significant amounts of an active antibacterial drug, triclosan, to inhibit the growth of bacteria. Because the micellar encapsulation of hydrophobic therapeutics does not require specific chemical interactions, we believe this noncovalent approach provides a new route to integrating active small, uncharged, and hydrophobic therapeutics into LbL thin films for biological and biomedical coatings.
ACS Nano 2008 Feb
PMID:Hydrogen-bonding layer-by-layer-assembled biodegradable polymeric micelles as drug delivery vehicles from surfaces. 1920 41

Solution-processable polyelectrolyte complexes (PECs) between poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) were synthesized in aqueous NaOH and obtained in their solid forms by protection and deprotection of carboxylic acid groups. Elemental analysis, conductance measurement, and FT-IR showed that the composition and ionic complexation degree (ICD) of the PECs can be controlled effectively by tuning the NaOH concentration in both parent polyelectrolyte solutions. Thermal gravity analysis showed that PECs revealed good thermal stability, and differential scanning calorimetry showed that the glass transition temperature (Tg) of PECs increased with increasing ICD and finally became undetectable when ICD was above 0.16. Viscosity properties of the PEC solutions were well correlated to the ICD of PECs, and it was found that solid PECs could be redissolved in dilute NaOH without breaking the ionic complexation between PDDA and PAA. Homogeneous PEC membranes (HPECMs) were made from their concentrated solutions, and their morphologies were examined by field emission scanning electron microscopy. These novel HPECMs were subjected to dehydration of organics for the first time, and a very promising performance was obtained. Furthermore, another two solution-processable PECs between weak anionic polyelectrolyte and cationic polyelectrolyte were also synthesized by the same method and showed a very high separation performance.
ACS Appl Mater Interfaces 2009 Jan
PMID:Synthesis and characterization of solution-processable polyelectrolyte complexes and their homogeneous membranes. 2035 59

We fabricated photopatternable and conductive polymer/multiwalled carbon nanotube (MWNT) composites by dispersing MWNTs with poly(4-styrenesulfonic acid) (PSS) and poly(acrylic acid) (PAA) in water. PAA enables photo-cross-linking in the composite by adding ammonium dichromate, and PSS assists the dispersion of MWNTs in the composites, leading to higher conductivity. Composite films of PAA/PSS-MWNTs were characterized by conductivities of 1.4-210 S/cm and a work function of 4.46 eV, which could be increased to 4.76 eV during UV photo-cross-linking. By using PAA/PSS-MWNT composites as source/drain electrodes, 6,13-bis(triisopropylsilylethynyl)pentacene field-effect transistors (FET) exhibited a field-effect mobility of 0.101 +/- 0.034 cm(2)/(V s), which is 9 times higher than that of FETs fabricated with gold as source/drain electrodes (0.012 +/- 0.003 cm(2)/(V s)).
ACS Appl Mater Interfaces 2009 Oct
PMID:Photopatternable source/drain electrodes using multiwalled carbon nanotube/polymer nanocomposites for organic field-effect transistors. 2035 70

Acrylic acid monomer in a viscous supporting nylon solution was polymerized and fabricated simultaneously via an electrospinning process. This novel polymerization method defines the fiber morphology as a network of interconnected mats. This network consists of smaller poly(acrylic acid) (PAA) fibers, approximately 19 nm in diameter, and larger nylon 6 fibers, approximately 75 nm in diameter. These two different fibers are separated by extraction of PAA from the fibrous mat in water and differentiation of field-emission scanning electron microscopy (FESEM) images of the same mat using before and after extraction of PAA. The structure of the extracted PAA was confirmed by 1H NMR and Fourier transform infrared (FT-IR) analysis. The observed modification to conventional electrospun mats is due to the presence of an extra phase-separated PAA produced by the electrospinning polymerization process. Finally, fiber morphologies and hybrid property were characterized via FT-IR, FESEM, thermogravimetric analysis, and X-ray diffraction. Similarly extracted samples and synthesis PAA were characterized in FT-IR and 1H NMR spectroscopy.
ACS Appl Mater Interfaces 2009 Apr
PMID:Synchronized polymerization and fabrication of poly(acrylic acid) and nylon hybrid mats in electrospinning. 2035 99

A new, efficient, palladium- and chromium-free process for the electroless plating of acrylonitrile-butadiene-styrene (ABS) polymers has been developed. The process is based on the ion-exchange properties of poly(acrylic acid) (PAA) chemically grafted onto ABS via a simple and one-step method that prevents using classical surface conditioning. Hence, ABS electroless plating can be obtained in three steps, namely: (i) the grafting of PAA onto ABS, (ii) the copper Cu(0) seeding of the ABS surface, and (iii) the nickel or copper metallization using commercial-like electroless plating bath. IR, XPS, and SEM were used to characterize each step of the process, and the Cu loading was quantified by atomic absorption spectroscopy. This process successfully compares with the commercial one based on chromic acid etching and palladium-based seed layer, because the final metallic layer showed excellent adhesion with the ABS substrate.
ACS Appl Mater Interfaces 2010 Apr
PMID:ABS polymer electroless plating through a one-step poly(acrylic acid) covalent grafting. 2036 51

Si-based Li-ion battery anodes offer specific capacity an order of magnitude beyond that of conventional graphite. However, the formation of stable Si anodes is a challenge because of significant volume changes occurring during their electrochemical alloying and dealloying with Li. Binder selection and optimization may allow significant improvements in the stability of Si-based anodes. Most studies of Si anodes have involved the use of carboxymethylcellulose (CMC) and poly(vinylidene fluoride) (PVDF) binders. Herein, we show for the first time that pure poly(acrylic acid) (PAA), possessing certain mechanical properties comparable to those of CMC but containing a higher concentration of carboxylic functional groups, may offer superior performance as a binder for Si anodes. We further show the positive impact of carbon coating on the stability of the anode. The carbon-coated Si nanopowder anodes, tested between 0.01 and 1 V vs Li/Li+ and containing as little as 15 wt % of PAA, showed excellent stability during the first hundred cycles. The results obtained open new avenues to explore a novel series of binders from the polyvinyl acids (PVA) family.
ACS Appl Mater Interfaces 2010 Nov
PMID:Toward efficient binders for Li-ion battery Si-based anodes: polyacrylic acid. 2105 20

The ligand induced electroless plating (LIEP) process was recently developed and thoroughly demonstrated with one of the most used polymers for plating processes: acrylonitrile-butadiene-styrene (ABS). This generic process is based, thanks to the use of diazonium salts as precursors, on the covalent grafting of a thin layer of poly(acrylic acid) (PAA) acting as ligand for metallic salts onto pristine polymer surfaces. This strategy takes advantage of the PAA ion exchange properties. Indeed, carboxylate groups contained in PAA allow one to complex copper ions which are eventually reduced and used as catalysts of the metallic deposition. Essentially based on ABS, ABS-PC (ABS-polycarbonate) and PA (polyamide) substrates, the present paper focuses on the role of the polymer substrate and the relationships between the macroscopic properties and microscopic characterizations such as infrared (IR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The adhesion strength of the metallic layer deposited via that LIEP process with the bulk polymer substrates was successfully compared with the adhesion of similar copper films deposited by the usual process based on chromic acid etching and palladium-based seed layer, by measuring the T-peel adhesion strength, and by carrying out the common industrial scotch tape test. Lastly, the electrical properties of the deposited layer were studied thanks to a four-point probe and scanning tunneling microscopy (STM) measurements.
ACS Appl Mater Interfaces 2010 Nov
PMID:Microscopic study of a ligand induced electroless plating process onto polymers. 2105 43

Graphene oxides (GO) were exfoliated in N,N-dimethylformamide by simple sonication treatment of the as-prepared high quality graphite oxides. By high-speed mixing of the pristine poly(amic acid) (PAA) solution with graphene oxide suspension, PAA solutions containing uniformly dispersed GO can be obtained. Polyimide (PI) nanocomposite films with different loadings of functionalized graphene sheets (FGS) can be prepared by in situ partial reduction and imidization of the as-prepared GO/PAA composites. Transmission electron microscopy observations showed that the FGS were well exfoliated and uniformly dispersed in the PI matrix. It is interesting to find that the FGS were highly aligned along the surface direction for the nanocomposite film with 2 wt % FGS. Tensile tests indicated that the mechanical properties of polyimide were significantly enhanced by the incorporation of FGS, due to the fine dispersion of high specific surface area of functionalized graphene nanosheets and the good adhesion and interlocking between the FGS and the matrix.
ACS Appl Mater Interfaces 2010 Dec
PMID:In situ thermal preparation of polyimide nanocomposite films containing functionalized graphene sheets. 2106 2


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