Joko Sutrisno

Sensing Behavior of Magnetorheological Elastomers

A magnetorheological elastomer (MRE) is comprised of ferromagnetic particles aligned in a polymer medium by exposure to a magnetic field. The structures of the magnetic particles within elastomers are very sensitive to the external stimulus of either mechanical force or magnetic field, which result in multiresponse behaviors in a MRE. In this study, the sensing properties of MREs are investigated through experimentally characterizing the electrical properties of MRE materials and their interfaces with external stimulus (magnetic field or stress/strain). A phenomenological model is proposed to understand the impedance response of MREs under mechanical loads and magnetic fields. Results show that MRE samples exhibit significant changes in measured values of impedance and resistance in response to compressive deformation, as well as the applied magnetic field.

Behavior of magnetorheological elastomers with coated particles

Iron particle coating can improve the behavior of magnetorheological elastomers (MREs) by inhibiting iron particle rusting; however, such a process can change physical properties of MREs such as oxidation resistance, shear modulus, and stiffness change due to an applied magnetic field. In this study, MRE samples are fabricated with regular and polymerized iron particles. To investigate the possibility and extent of these changes, polymerized particle MRE samples are made using a combination of reversible addition fragmentation chain transfer and click chemistry. Shear test sample MREs with pure elastomer and 50 wt% MRE with and without polymerization are fabricated. To observe the effect of oxidation on shear properties of MREs, pure elastomer and 50 wt% coated and non-coated samples are oxidized using accelerated oxidation procedure. Experimental results show that oxidation significantly reduces the shear modulus of the elastomer matrix. The coating process of iron particles does not significantly change the shear modulus of resulting MREs but reduces the loss of shear modulus due to oxidation.

Electrical Properties of Magneto-Rheological Elastomers

A magnetorheological elastomer (MRE) is comprised of ferromagnetic particles aligned in a polymer medium by exposure to a magnetic field. The structures of the magnetic particles within elastomers are very sensitive to the external stimulus of either mechanical force or magnetic field, which result in multi-response behaviors in MRE. In this study, sensing properties of MREs through experimentally characterizing the electrical properties of materials and theirs interfaces with external stimulus (magnetic field or stress/strain) are investigated. A phenomenological model is proposed to model the impedance response of MREs. Results show that MRE samples exhibit significant changes in measured values of impedance and resistance in response to compressive deformation, as well as applied magnetic field.Copyright

Laser irradiation of ferrous particles for hyperthermia as cancer therapy, a theoretical study

Our recent in vivo animal studies showed the feasibility of using micron sized iron particles to induce physical damage to breast cancer tumors and thereby triggering a localized immune response to help fight the cancer. Combining a hyperthermic treatment with this ongoing study may enhance the immune response. As a result, a novel treatment of inducing hyperthermia using iron particles excited by a continuous wave near-infrared laser was analyzed. In this theoretical study, Mie scattering calculations were first conducted to determine the absorption and scattering efficiencies of the suspended drug coated particles. The resulting heat transfer between the particles and the surrounding tumor and the healthy tissue was modeled using Pennes’ Bioheat equation. Predicted temperature changes were satisfactory for inducing hyperthermia (42∘C), thermally triggering drug release, and even thermal ablation (55∘C).

Surface Modification of Heteropolyacids (HPAs) for Proton Exchange Membrane Fuel Cells (PEMFCs)

Novel composite proton exchange membranes have been prepared from surface modification of heteropolyacids, namely: silicotungstic acid (SiWA), and sulfonated poly(ether ether ketone) (SPEEK) as a polymer matrix. Atom transfer radical polymerization (ATRP) has been used for surface polymerization of sodium 4-vinyl benzene sulfonate (S4VBS) on SiWA. PEEK has been sulfonated using chlorosulfonic acid. The major outcome of this work was surface coated SiWA–poly(S4VBS) which resulted in homogenous composite membranes as compared with non-surface coated SiWA. The thermal properties of surface polymerized S4VBS have been characterized using differential scanning calorimetry (DSC). The SiWA particles and cross section of the composite membrane have been imaged using DSC. Composite membrane conductivity has been characterized using electrochemical impedance spectroscopy. This route was expected to provide a membrane with high conductivity because of the presence of sulfonic acid groups on the grafted polymer backbone, and to avoid “washing out” of HPA in the fuel cell.

Synthesis and characterization of surface‐grafted poly(N‐isopropylacrylamide) and poly(carboxylic acid)—Iron particles via atom transfer radical polymerization for biomedical applications

This research relates to the preparation and characterization of surface grafted poly(N-isopropylacrylamide) and poly(carboxylic acid)-micron-size iron particles via atom transfer radical polymerization (ATRP). The surface grafted polymers-iron particles result in multifunctional materials which can be used in biomedical applications. The functionalities consist of cell targeting, imaging, drug delivery, and immunological response. The multifunctional materials are synthesized in two steps. First, surface grafting is used to place polymer molecules on the iron particles surface. The second step, is conjugation of the bio-molecules onto the polymer backbone. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy were used to confirm the presence of polymers on the iron particles. The thickness of the grafted polymers and glass transition temperature of the surface grafted polymers were determined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The covalent bond between grafted polymers and iron particles caused higher glass transition temperature as compared with non-grafted polymers. The ability to target the bio-molecule and provide fluorescent imaging was simulated by conjugation of rat immunoglobulin and fluorescein isothiocyanate (FITC) labeled anti-rat. The fluorescence intensity was determined using flow cytometry and conjugated IgG-FITC anti-rat on iron particles which was imaged using a fluorescence microscopy.