Swelling of ferrogels in uniform magnetic field - A theoretical approach

Magnetic field sensitive gels (ferrogels or magnetoelasts) are three-dimensional cross-linked networks of flexible polymers swollen by ferrofluids or magnetic fluids. The influence of external magnetic field on the equilibrium swelling degree is the subject of this study. Using thermodynamic arguments it is shown that uniform external field may result in deswelling of the ferrogels at high field intensities

Rheological Behaviour of Pigment Filled Polymer Dispersions: The influence of electric field

Rheological properties of materials are related to their response to applied stress. The field induced chain formation of a large number of organic and inorganic substances such as starch, aluminium oxide, ferric oxide, carbon black, ion-exchange resins, and polymer powders have been studied mainly in insulating oils. Much less is studied and understood the electrorheological effect of pigments in polymer dispersions. Titanium dioxide is one of the most frequently used surface coatings due to its high-quality and ecologically acceptable properties. In the present paper the authors first review the basic principle of electrorheology, then it is followed by experimental studies on structuring and rheological properties

Electric field controlled flow behaviour of electrorheological fluid

The main purpose of the present study is to demonstrate the electric field controlled flow behaviour of electrorheological (ER) fluid. We have investigated the relation between the electric field and the change in the viscosity of electrorheological fluids. Different kinds of suspensions are used to search for the proper combination ER fluid for applying in a motor mount. A rotational viscometer is used to get how the viscosity depends on temperature and a special device to measure the effect of electric fields up to 1.8 kVmm-1

Intelligens lágy anyagok kutatása = Intelligent soft materials

Intelligens lágy anyagok kutatása című OTKA pályázat keretén belül az alábbi feladatokat végeztük el: 1. Új típusú elektroreológai(ER) -, és/vagy magnetoreológiai (MR) folyadékok, valamint hasonló elven alapuló gélek és lágy gumik előállítása. Homogén elektromos vagy mágneses térben a folyadékfázisban diszpergált részecskékből láncszerű aggregátumok képződnek. Ezt a struktúrát kémiai módszerekkel rögzítve anizotrop anyagokat állítottunk elő. Anizotróp elasztomerek előállítása mellett szisztematikus mechanikai és duzzadáskinetikai vizsgálatokat végeztünk. 2. Hőmérsékletérzékeny NIPA gél fázisátalakulásán alapuló, termikusan változtatható fényáteresztő-képességű intelligens üvegeket állítottunk elő. A gélkollapszust követő térfogatcsökkenés kiküszöbölésére interpenetrációs NIPA/PVA gélrendszereket fejlesztettünk ki. 3. Olyan gél-rendszerek fejlesztettünk ki, amelyeknél az model hatóanyag leadás a gélkollapszus jelensége alapján a diffúziótól függetlenül, termikus hatással szabályozható. 4. Az alumínium- és sziliciumtartalmú hibrid gélek állítottunk elő és vizsgáltunk speciális tulajdonságú (pl igen kis sűrűségű piezoelektromos) anyagok előállítása céljából. Az előállításánál kiindulási anyagként tetraetoxi-szilán, alumínium-nitrát és a PDMS-ból álló kompozitot használtunk. A szervetlen fázis előgélesítésének ideje és a PDMS molekulák mérete erősen befolyásolja a kialakuló hibrid gél kötésrendszerét, szerkezetét és tulajdonságait. | Intelligent Soft materials The following works have been carried out in the last four years:1.Preparation of magnetic and electric field sensitive anisotropic PDMS elastomers and gels using new type of silicon oil based magneto- and electrorheological fluids. In uniform field the dispersed particles formed chain-like structure. This particles formation can be fixed in the polymer matrix by cross-linking chemical reaction resulting anisotropic samples. Systemic mechanical and swelling kinetics measurements were performed on these anisotropic samples. 2.Based on the phase transition of temperature sensitive NIPA gel, intelligent gel-glass with controllable light transparency was developed. In order to reduce the volume change, interpenetration NIPA/PVA network was developed. 3.New thermoresponsive composite-gel membranes capable of regulating permeability in response to external temperature were prepared. These membranes containing ordered nano channels can act as ?on - off? switches or ?permeability valves?. 4.Hybrid gels with aluminium and silicon contains were prepared and investigated in order to develop special materials (e.g.: with very low density and piezoelectric property). Tetraetoxy-silan, aluminium-nitrate and PDMS were used to fabricate composite materials. The pregelation time of the inorganic phase and size of the PDMS chains have a significant influence on the structure and on the property of the formed hybrid gel

Mágneses és elektromos térre érzékeny kompozit gélek és elasztomerek = Magnetic an electric field responsive composite polymer gels and elastomers

Mágneses és elektromos térre érzékeny kompozit gélek és elasztomerek előállítása című ifjúsági OTKA pályázat keretén belül az alábbi feladatokat végeztük el: Új típusú elektromos illetve mágneses térre érzékeny anizotrop PDMS elasztomereket állítottunk elő. Az anizotrop elasztomerek térfüggő mechanikai tulajdonsággal rendelkeztek. Homogén mágneses tér segítségével az elasztomerek rugalmassága szabályozható. Sikerült olyan mágneses elasztomert előállítani, ahol a rugalmassági modulusz homogén mágneses tér hatására pillanatszerűen, reverzibilis módon 300 %-kal növekedett. Tanulmányoztuk az anizotrop PDMS gélek duzzadási tulajdonságait. Duzzadáskinetikai mérések során megállapítottuk, hogy a vasat tartalmazó anizotrop rendszerek izotrop, míg a vas-oxidot tartalmazó rendszerek anizotrop módon duzzadtak ciklohexánban. Új, külső hatással szabályozható permeabilitású membránt állítottunk elő, amelyben nano méretű csatornákat építettünk be. A gélmátrixba ágyazott, nanométer tartományba eső gél részecskék mérete környezeti hatásokkal (pl. hőmérséklettel, pH-val, mágneses térrel) széles határok között, pillanatszerűen változtatható. A lánc-szerű füzérekbe rendezett gélgömbök fentebb felsorolt hatásokkal előidézett méretváltozása jelenti a membrán nyitó-záró mechanizmusát, amely megteremti a lehetőségét a külső hatásokkal szabályozható hatóanyag leadásnak. | Preparation of magnetic and electric field sensitive composite gels and elastomers The following works have been carried out int he last two years: 1. Preparation of magnetic and electric field sensitive anisotropic poly(dimethyl-siloxane) elastomers using silicon oil based magneto- and electrorheological fluids. The anisotropic magnetoelasts showed direction dependent elastic modulus. In external uniform magnetic field the elastic modulus of the sample can be reversible increased up to 300%. 2. Swelling kinetics experiments were performed on the anisotropic magnetoelast in cyclohexane. It was concluded that the elastomers filled with iron particles swelled isotopic way in contradiction to the iron-oxide loaded elastomers which swelled anisotropicly. 3. New thermoresponsive composite-gel membranes capable of regulating permeability in response to external temperature were prepared. These membranes containing ordered nano channels can act as "on - off" switches or "permeability valves". The channels are designed to contain an ordered array of stimuli responsive core-shell type gel beads that can change their size in response to external stimuli. Expansion and contraction of the thin shell of hydrogel coated magnetic polystyrene latex particles ordered in arrays affect the permeation pattern from the membrane "on" state to "off" state. The duration and rate of mass transfer can be controlled by temperature

Magneto-sensitive elastomers in a homogeneous magnetic field: a regular rectangular lattice model

A theory of mechanical behaviour of the magneto-sensitive elastomers is developed in the framework of a linear elasticity approach. Using a regular rectangular lattice model, different spatial distributions of magnetic particles within a polymer matrix are considered: isotropic, chain-like and plane-like. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. At the same time, with increasing magnetic field the Young's modulus for tensile deformation along the magnetic field decreases for both chain-like and isotropic distributions of magnetic particles and increases for the plane-like distribution of magnetic particles.Comment: 38 pages, 15 figure

Multifunkcionális polimer gélek és kompozitok kifejlesztése = Development of multifunctional smart polymer gels and composites

Ferromágneses vagy szuperparamágneses CoO és Co3O4 nanoporok oldatfázisú szintetizálása felületaktív anyagok jelenlétében történt vagy termikus bontással kombinált lecsapásos vagy szol-gél módszerrel. A szol-gél módszer etil-acetát és 1-propanol keverékében eredményezte a legkisebb méretű (átlagosan 85 nm-es) és polidiszperzitású (70-100 nm), egységes alakú, gömbszerű részecskéket. Vizes és organikus közegű stabil mágneses és elektroreológiai folyadékokat is előállítottunk. Vizsgáltuk a reológiai tulajdonságaikat: annak ellenére, hogy az elektro- és magnetosztatika törvényei alapján homogén sztatikus térben hasonló reológiai viselkedés várható, mégis található olyan jelenség, amely – jelenlegi ismereteink szerint - csak az elektroreológia folyadékoknál lép fel. Ilyen például az elektrokonvekció, vagy az általunk részletesen tanulmányozott részecske elektrorotáció. Mágneses- és elektromos térre érzékeny kolloid részecskéket rugalmas polimerbe és polimer gélbe építettük be. Izotróp és anizotróp géleket egyaránt szintetizáltunk, és vizsgáltuk ezek mechanikai és termodinamikai tulajdonságait. Poliszukcinimid- és poliaszparaginsav alapú géleket szintén készítettünk és tanulmányoztuk ezek gélkollapszuson alapuló nyitó-záró mechanizmusát. Vizsgáltuk a duzzadásfok változásának nagyságát, valamint a folyamat kinetikáját. A hálóláncok hidrofil/hidrofób jellegét különböző polaritású molekulák főlánchoz történő ojtásával multifunkcionális polimer géleket lehetett szintetizálni. | In the present work, CoO and Co3O4 nanoparticles were synthesized by various liquid-phase methods, namely, coprecipitation and sol-gel techniques combined with thermal decomposition. The best result (130-230 nm) could be achieved by application of cobalt nitrate, a carbonate agent and PDMS of 550 g mol-1. In the sol-gel procedures, the use of ethyl acetate yielded the finest particles with mean diameter of 85 nm and a narrow polydispersity (70-100 nm). The sol-gel method results in more spherical shaped and uniform particles, than those produced by coprecipitation. We have prepared magnetorheological and electrorheological fluids and studied the rheological behaviour as a function of external applied field. Isotropic and highly anisotropic magnetic field responsive gels were prepared and the deformation and the swelling under external fields were investigated on the basis of thermodynamic arguments. Chemically cross-linked poly(aspartic acid) (PASP) gels were prepared by the hydrolysis of poly(succinimide) (PSI). The PSI chains were cross-linked by natural amines and amino acid derivatives to obtain biodegradable, biocompatible hydrogels. The gels show a volume phase transition around the pK values of PASP. The most important network parameters were determined by a modified version of the Brannon–Peppas–Peppas theory. Kinetics of hydrolysis induced swelling as well as pure swelling of PSI and PASP gels were studied

Physical effects upon whey protein aggregation for nano-coating production

Production of edible nanostructures constitutes a major challenge in food nanotechnology, and has attracted a great deal of interest from several research fields — including (but not limited to) food packaging. Furthermore, whey proteins are increasingly used as nutritional and functional ingredients owing to their important biological, physical and chemical functionalities. Besides their technological and functional characteristics, whey proteins are generally recognized as safe (GRAS). Denaturation and aggregation kinetics behavior of such proteins are of particular relevance toward manufacture of novel nanostructures possessing a number of potential uses. When these processes are properly engineered and controlled, whey proteins may form nanostructures useful as carriers of bioactive compounds (e.g. antimicrobials, antioxidants and nutraceuticals). This review discusses the latest advances in nano-scale phenomena involved in protein thermal aggregation aiming at formation of bio-based nano-coating networks. The extent of aggregation is dependent upon a balance between molecular interactions and environmental factors; therefore, the impact of these conditions is addressed in a critical manner. A particular emphasis is given to the effect of temperature as long as being one of the most critical variables. The application of moderate electric fields (MEF), an emergent approach, as such or combined with conventional heating is considered as it may inhibit/prevent excessive denaturation and aggregation of whey proteins — thus opening new perspectives for development of innovative protein nanostructures (i.e. nano-coatings). A better understanding of the mechanism(s) involved in whey protein denaturation and aggregation is crucial as it conveys information relevant to select methods for manipulating interactions between molecules, and thus control their functional properties in tailor-made applications in the food industry.Oscar L. Ramos and Ricardo N. Pereira gratefully acknowledge Post-Doctoral grants (SFRH/BPD/80766/2011 and SFRH/BPD/81887/2011, respectively) by Fundacao para a Ciencia e Tecnologia (FCT, Portugal). All authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013 and Project "BioEnv - Biotechnology and Bioengineering for a sustainable world", REF. NORTE-07-0124-FEDER-000048, co-funded by Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER

Design of bio-nanosystems for oral delivery of functional compounds

Nanotechnology has been referred to as one of the most interesting topics in food technology due to the potentialities of its use by food industry. This calls for studying the behavior of nanosystems as carriers of biological and functional compounds aiming at their utilization for delivery, controlled release and protection of such compounds during food processing and oral ingestion. This review highlights the principles of design and production of bio-nanosystems for oral delivery and their behavior within the human gastrointestinal (GI) tract, while providing an insight into the application of reverse engineering approach to the design of those bio-nanosystems. Nanocapsules, nanohydrogels, lipid-based and multilayer nanosystems are discussed (in terms of their main ingredients, production techniques, predominant forces and properties) and some examples of possible food applications are given. Phenomena occurring in in vitro digestion models are presented, mainly using examples related to the utilization of lipid-based nanosystems and their physicochemical behavior throughout the GI tract. Furthermore, it is shown how a reverse engineering approach, through two main steps, can be used to design bio-nanosystems for food applications, and finally a last section is presented to discuss future trends and consumer perception on food nanotechnology.Miguel A. Cerqueira, Ana C. Pinheiro, Helder D. Silva, Philippe E. Ramos, Ana I. Bourbon, Oscar L. Ramos (SFRH/BPD/72753/2010, SFRH/BD/48120/2008, SFRH/BD/81288/2011, SFRH/BD/80800/2011, SFRH/BD/73178/2010 and SFRH/BPD/80766/2011, respectively) are the recipients of a fellowship from the Fundacao para a Ciencia e Tecnologia (FCT, POPH-QREN and FSE Portugal). Maria L. Flores-Lopez thanks Mexican Science and Technology Council (CONACYT, Mexico) for PhD fellowship support (CONACYT Grant number: 215499/310847). The support of EU Cost Actions FA0904 and FA1001 is gratefully acknowledged