M. Stamm
Leibniz Institut für Polymerforschung Dresden, Germany
stamm / ipfdd.de
The knowledge of structure and organization of polymers at nanoscale is important for the understanding of their properties - and offers interesting routes for the design of improved and new polymer based materials. In particular self-organisation processes can be used to generate nanostructured templates in thin films.
The microphase separation of diblock copolymers into well ordered nanostructures is an example, where polymer self-organization can be used for design of nanomaterials /1/. By proper selection of the copolymer, solvent and a low molecular weight additive, thin film templates with e.g. hexagonal order in the surface can be produced. When the additive is removed, ordered nanoscale empty cylinders can be generated, which serve as a template for metal depostion. Thus thin metalluic nanocylinders are produced which are arranged in hexagonal order on a solid substrate. By metal sputtering the deposition of metallic nanoclusters is possible, while also optically active components for deposition can be used. The nanotemplates from copolymers thus offer several possibilities for nanodevice formation.
This work is supported by DFG in the framework of the priority program "Nanowires and Nanotubes" .
/1/ A. Sidorenko, I. Tokarev, S. Minko, M. Stamm, JACS 125 (2003) 12211
A. Anderssona, K. DeSitterb, R. Leysenb, S. Mullensb, I.F.J. Vankelekomc , F.H.J. Maurera
aDepartment of Polymer & Materials Chemistry, Lund Institute of Technology, Lund University, P.O. Box 124, SE-22100 Lund, Sweden
bFlemish Institute for Technological Research (VITO), Boeretang 220, B-2400 Mol, Belgium
cCentre for Surface Chemistry and Catalysis, Faculty of Applied Bioscience and Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium
Polymer membranes in the gas separation industry have attracted much interest over the past decades. Rigid glassy polymer with high free volume and large free volume sites are of particular interest due to their capabilities for vapor separation applications like the removal of higher hydrocarbons from hydrogen streams and the recovery of organic vapors from process streams. The incorporation of nanofillers in these rigid polymers is a possible route to overcome the limitations of the commonly accepted permeation and selectivity interrelation.
The free volume sizes and interstitial mesopore sizes in poly (4-methyl-2-pentyne) (PMP) and poly(1-trimethylsilyl-1-propyne) (PTMSP)/silica nanocomposites were studied by Positron Annihilation Lifetime Spectroscopy (PALS). Correlations between gas permeability and changes of free volume structure and the existence of mesopores in nano-filler aggregates have been explored which play an important role in controlling the performance of the mixed matrix polymer membranes.
In the light of the promising but not fully understood increase of permeability and sometimes increased selectivity, it is important to gain more insight in the structure and performance of PMTP and PMP nanocomposites.
M. Furukawaa, K. Kojiob
aDepartment of Materials Science, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki, 852-8521, Japan (furukawa / nagasaki-u.ac.jp, http://www.mase.nagasaki-u.ac.jp/lab/kouji/KOUEng.htm), b Department of Materials Science and Engineering, Faculty of Engineering, Nagasaki University, Japan
Introduction: It is well known that the polyurethane elastomers(PUEs) consist of the hard segment and soft segment, and exhibit microphase-separated structure. It is expected that the strong polar groups will help to form stable film even at a molecular level and strongly affect the microstructure of the polymer films. Also, the multiblock structure will restrict the segregation of lower surface free energy components at the film surface, resulting in the formation of the lateral phase separation. Here, we report the novel factor, “film thickness” for the controlling the size of microphase separation.
Experimental; PUE with the hard segment content of 34 wt% are synthesized from with poly(oxytetramethylene)glycol (PTMG), 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) by a prepolymer method. The ultra thin films were prepared onto a silicon wafer from the tetrahydrofuran PUE solution by a spin coating method. The bulk and thin films are characterized using the ATR-FT-IR spectra and AFM image.
Results and Discussion; In the AFM phase images of the PUE films for the thickness of 200 and 6 nm, microphase-separated structure, which consists of the hard segment domains (darker portion) and soft segment matrix (brighter matrix), was clearly observed. The size of microphase-separated structure seems to be different depending on the film thickness. The domain spacing for bulk and the thicker film (~200 nm) was ca. 20 nm, while that for the ultra thin film below 8 nm dramatically decreased to ca. 10 nm. This result suggests to be simply related to a decreasing space. We found that the phase-separated domain size of block copolymer decreased with decreasing film thickness.
H. Galina*, J.B. Lechowicz, M. Walczak
Rzeszów University of Technology, Faculty of Chemistry, Department of Industrial and Materials Chemistry, ul. W. Pola 2, 35-959 Rzeszów, Poland (hgal / prz.edu.pl)
The process of room temperature polycondensation using carbodiimide-coupling reagent in the presence of suitable catalyst (4-(N,N-dimethylamino)pyridinium 4-toluenesulfonate) has been developed. Aliphatic-aromatic polyesters from 4,4-bis(4-hydroxyphenyl)pentanoic acid were synthesized. The hyperbranched polyesters were characterized by GPC equipped with a multiple detector consisting of refractometer, differential viscometer and right angle laser light scattering photometer. Intrinsic viscosity, hydrodynamic radius and radius of gyration of hyperbranched polyesters were measured. The course of polyesterification reaction was followed by 1H NMR spectroscopy.
The molecular size distribution of the hyperbranched polymers was controlled by: (i) using bisphenol A as a 'core' molecule in the amount of 5 or 10 mol-%, (ii) introducing monomer to the core in several portions of the same or different sizes, (iii) adjusting the conversion of functional groups at each addition of monomer. The results were confronted with model calculations performed by using a kinetic method.
The hyperbranched polyesters prepared by low-temperature polymerization mimic those prepared conventionally by the melt polymerization. As resembling more regular dendrimers, they have potential applications as nanocapsules, nanosorbents, nanomicelles or polymer network/star precursors.
P. Pissis
National Technical University of Athens, Zografou Campus, 15780, Athens, Greece (ppissis / central.ntua.gr)
There is yet no satisfactory theoretical explanation for the significant improvement of properties often observed in polymer nanocomposites at very low filler contents. It is generally agreed upon, however, that interfacial effects arising from polymer-filler interactions play a significant role. Molecular dynamics simulations show that in the vicinity of a solid surface polymer dynamics becomes faster or slower depending on the type and strength of interaction and the roughness of the surface. Guided by theory and by results obtained with model systems of geometrical confinement, we have investigated over the last few years molecular dynamics in polymer nanocomposites with various matrices (thermoplastics, thermosets, rubbers) and fillers (silica, carbon nanotubes, fullerenes, POSS). To that aim we employ dielectric techniques (broadband dielectric relaxation spectroscopy - DRS and thermally stimulated depolarization currents - TSDC) and, to a lesser extend, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Results for polymer dynamics are correlated with results of structural and morphological characterization.
DSC results are evaluated in terms of variation of the glass transition temperature in the nanocomposites with respect to the bulk (pure matrix). They often reveal the existence of a fraction of polymer immobilized on the surface of the nanoparticles. Broadband DRS measurements, analyzed in terms of time scale, relaxation strength and shape of the response, enable to follow effects of the nanoparticles on the secondary (local relaxations) and, in particular, on the segmental α relaxation associated with the glass transition. For polymers having a dipole moment component along the chain contour an additional relaxation of larger length scale, the normal mode relaxation, is active. Electrical conductivity studies prove effective for morphological characterization, as the moving ions probe the local morphology. TSDC techniques enable to experimentally study distributions of relaxations times of the modified (interfacial) polymer corresponding to distributions of glass transition temperatures.
Several examples will be presented demonstrating effects of the degree of dispersion of nanoparticles and the type and strength of polymer-filler interaction (chemical bonding, hydrogen bonding, Van der Waals interaction) on polymer dynamics. Results obtained by various techniques will be compared with each other, allowing conclusions on the nature of motion probed by each technique.
V. Choudhary
Centre for polymer Science and Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi-16 , India
Cancer is the third most common disease in the world. Breast cancer is the most common malignancy affecting women, with more than one million cases occurring worldwide annually. Most of anticancer drugs have marginal selectivity for cancerous cells because they target cells which are replicating at high proliferation rate. Thus anticancer drugs have high toxicity against rapidly dividing normal cells. Tumor blood vessels have several abnormalities compared to normal vessels. Transport of anticancer drug is governed by physiological (pressure) and physiochemical (composition, structure) properties of interstitum and drug molecule (size, configuration, charge, hydrophobicity). Physiological barrier in tumor region (i.e. poorly vascularised tumor region, acidic environment, high interstitial pressure and low microvascular pressure) as well as cellular levels (altered activity of specific enzymes) and in body (i.e. biodistribution and clearance of anticancer agent) must be overcome to deliver anticancer agents to tumor cells in vivo. Colloidal nano-particles incorporating anticancer agents can overcome such resistance to drug action, increase selectivity towards cancer cells and reduce their toxicity towards normal cells. Controlled release inside tumors can be obtained by regulating structure of nanoparticles, polymers used and method of incorporation of drug molecule (adsorption or encapsulation). Nanoparticles loaded with anticancer agents can successfully increase the drug concentration in cancer tissue and also act at cellular levels and can enhance anticancer efficiency.
The paper describes the preparation and characterization of novel nanoparticles/nanogels using thermoresponsive polymers for targeted drug delivery. Nanoparticles having core-shell morphology were prepared by copolymerizing N-isopropyl acrylamide with varying amounts of poly(ethylene glycol) methacrylate (PEGMA) of varying molecular weight ranging from 526 g/mol to 2000 g/mol. The nanoparticles were synthesized by dispersion polymerization using ammonium persulfate as an initiator at 80 0C (much above the LCST). The effect of reaction conditions i.e. temperature, concentration of initiator, temperature, monomer feed composition and time of polymerization was investigated. Particle size and size distribution was determined using light scattering method. Stability of emulsions was also established. Particle size decrease with increasing amounts of PEGMA in the feed as well as with initiator amount.
The polymeric particles having an optimum particle size and LCST close to body temperature were further modified by preparing folic acid conjugates. MCF-7 cancer cell lines were used to evaluate the performance of these nanoparticles. The proposed approach provides a better and more effective site-specific method of drug delivery to improve the efficacy of highly cytotoxic anticancer drugs.
Elastomeric materials are often compounded with reinforcing fillers to improve their mechanical properties. The effectiveness of a filler depends on filler characteristics such as size and shape of the particles and more significantly on the strength of polymer-filler interactions. Theses interactions increase the effective degree of cross-linking and such an effect is particularly strong if the particle have some reactive surface groups.
The extent of reinforcement increases as the particle size decreases leading to a higher polymer-filler interface and thus a more efficient interfacial bond provided that a certain degree of bonding exists between the two phases. Reinforcing fillers have usually particle diameters in the range of 10 to 100 nm.
The shape of the inclusions is also expected to affect the properties of the composites. The effect can be pronounced for highly anisotropic particles such as needles where a preferred orientation could modify the deformation behavior.
The state of dispersion is considered to be of crucial importance for the mechanical properties of the polymer composites. Filler aggregates tend to associate to form agglomerates, especially at high filler loadings. Recently the sol-gel technique that can generate in-situ reinforcing particles, has been widely applied for the synthesis of hybrid organic-inorganic materials. This process, which consists of hydrolysis and condensation of an alkoxysilane such as tetraethoxysilane (TEOS) is expected to yield small and well-dispersed particles within the polymer matrix. The structure and morphology of the filler depend on the reaction conditions and essentially on the nature of the catalyst.
Nanosized fillers with high aspect ratio presents both advantages of a low percolation threshold and an important interface area. Naturel rubber, filled with nanofibers of sepiolite or multiwall carbon nanotubes (MWNT), display high levels of reinforcement at low filler loadings. On the other hand, the formation of a percolating network, evidenced by a strong decrease in resistivity, occurs between 2 and 3 phr (phr = parts per hundred parts of rubber) for MWNT-filled samples.
The goal of this paper is to review the mechanisms responsible of the reinforcement effect and to compare the extent of reinforcement provided by different types of fillers : conventional fillers, particles generated in situ by the sol-gel process, layered and fibrous clays and carbon nanotubes.
J. Jančář, J. Kalfus
Institute of Materials Chemistry, Brno University of Technology, Brno, Czech Republic
Fundamental principles of polymer physics were used for description of relaxation behavior of a flexible polymer chain near solid weakly attractive surface in order to elucidate reinforcing mechanism introduced via adding nanosized particles into thermoplastic polymer matrix. Due to large specific surface area of the nanofillers ranging from 100 to 1000 m2/g, considerable portion of polymer matrix is in contact with the filler surface even at very low filler volume fractions. In this paper, nanocomposite was considered as a two component system consisting of a bulk polymer matrix and effective core-shell nanoparticles composed of adsorbed polymer shell and filler particle core. Chains in both polymer phases, i. e., in the bulk and in the immobilized layer, are able to relax the imposed external stress, however, each of them on a different time scale. The main objective of this paper is to elucidate the relaxation behavior of flexible polymer chains in nanocomposite above Tg of the neat matrix using the reptation concept. Above the Tg of the neat matrix, the chains in the bulk undergo free and chains in the immobilized layer near filler surface undergo retarded reptation dynamics due to the adsorption/desorption processes on the filler surface. The relaxation time was calculated for each phase using the Doi-Edwards reptation theory. To calculate the response of the whole polymer nanocomposite, a simple rule of mixtures model and percolation models were used. Calculated composite relaxation times were correlated with experimental modulus recovery data measured after the Payne effect in poly(vinylacetate)-hydroxyapatite nanocomposite. Good agreement was found between theoretical predictions and experimental data over the interval of nanofiller volume fraction ranging from 0 to 0.05.
AcknowledgementsThis research was funded by the Ministry of Education, Youth and Sports under the grant MSM 0021630501 which is greatly appreciated. Support from the NANOFUN POLY Consortium funded by the EC under the 6th Framework Program is also appreciated.
W.D. Cook*, G. Liang*, H.J. Sautereau#, A. Tcharkhtchi+
* Monash University, Australia
# INSA-Lyon, France
+ ENSAM-Paris, France
Many thermoplastics are highly viscous which can become a significant problem in processing, particularly when used with nano-fillers. The processes of rotomoulding, composite fabrication, powder coatings, injection moulding and extrusion are all used for thermoset and thermoplastic polymer production. Each technique is critically dependent on the changes in flow (rheology) occurring during processing and in many cases this imposes limits on the processibility and properties of the moulding. In this paper we will discuss the effect of addition of reactive plasticizers (thermosets) on the rheology, structure development, processibility and final properties of thermoplastics and their nano-composites. Two systems are under investigation. One uses a diallyl momomer as the reactive for clay nanocomposites of PVC and PC because its polymerization is slow and it has a high gel point conversion which aids in its process at elevated temperatures. The second uses a di-epoxy resin cured with an imidazole catalyst.
Department of Polymer Engineering, University of Akron, Akron, OH 44325 USA. (msoucek / uakron.edu, http://www.poly-eng.uakron.edu/soucek.htm )
There are a variety of factors that control the size and morphology of inorganic/organic hybrid systems. For inorganic/organic hybrid systems in which the organic phase is the continuous phase and the inorganic phase is formed in situ, reaction kinetics are important for defining and controlling phase morphologies. For UV-curable systems, the speed of reaction leads to interesting bimodal morphologies. Another key factor is mobility of the phases. The mobility of the phases for thermally cured systems are controlled by the temperature differential between the glass transition of the continuous phase and the temperature of curing. A third factor is coupling agents. It is proposed that coupling agents provide nucleation sites for inorganic phase growth. Also, coupling agents can provide a physical template for uniform dispersion of the inorganic phase. These factors and others can be used to create different morphologies and sizes of the inorganic phase from nano through meso to macrocomposites.
Fraunhofer Institut für Silicatforschung, Neunerplatz 2, 97082 Würzburg, Germany (michael.popall / isc.fraunhofer.de
Structures in microelectronic as well as photonic components move more and more towards the nano-scale. Using hybrid materials, this implies controlling the inorganic-organic nano-structural units. On the one hand e. g. low-k or high-k materials are searched for, but on the other hand being in dimensions much less than 100 nm the classical way of nano-particles in polymer matrix cannot be the choice. Reflecting the needs of nano-patterning technologies like extreme extreme-UV-lithography, femto-laser- or nano-imprint-technology the inorganic and organic units have to be chemically connected on molecular scale. There is not only a need for nano-structured layers in the components but most of the microelectronic and micro-optical systems nowadays additionally require a high integration level i. e. µm-resolved packaging. The driving forces are mobile applications or limited space in multi-media, sensing or safety devices. A better defined and reproducible build-up of nano-structured matrices based on nano-building-blocks or clusters with reactive functions therefore is searched for. Although the materials are highly sophisticated they have to be as cheap as possible to use them in mass production. The systematic use of standard characterisation methods in combination with NMR-spectroscopy and computational visualisation tools lead to a focused optimization of in-situ at much lower cost produced silsesquioxane-mixtures. In addition the latter method allows some hints about most reasonable position of the reactive organic functions for nano-resolved cross-linking. Examples in the field of microelectronic, photonic and polymer-electronic will be given.