Poly Methyl Methacrylate Matrices Research Articles

Influence of Tm+3 concentration on the non-linear optical effects of the BiB3O6 : Tm3+ glass nanoparticle-doped polymer

It is shown that BiB3O6 : Tm3+ glass nanoparticles incorporated into polymethylmethacrylate (PMMA) and polycarbonate (PC) polymer matrices show good second-order susceptibilities under bicolour coherent laser treatment. It is found that only during incorporation into highly polarized PC matrices could one observe an enhancement of the second-order susceptibilities with increasing laser treated power densities. The main increase is observed for all samples at power densities equal to about 0.4 GW cm−2. After passing this value there is a saturation of the output susceptibilities and even an abrupt decrease. The most striking feature is the achievement of second-order susceptibilities equal to about 5 pm V−1 for samples containing 4% nanoparticle (NP) content in the PC matrix. A further increase in the NP concentration to 6% leads to a decrease in susceptibility to 15%. In the case of PMMA matrices these changes do not exceed the background. The same situation is present for the pure BIBO and low-doped Tm materials. The effect is maximal for a low concentration of Tm—about 0.75%. In the case of bulk glasses the intensity dependences of the second-harmonic generation unambiguously show that the achieved maximal values of second-order susceptibilities do not exceed 3 pm V−1 for 0.5% Tm concentration.

PMMA-PQ Photopolymers for Head-Up-Displays

We present the experimental realization of a head-up-display based on a photopolymer. A phase volume reflection hologram is written in a photopolymer layer and is used as a screen for a signal beam. To write efficient holograms in the polymeric material we used ordinary and modified polymethylmethacrylate matrices containing phenanthrenequinone (PQ). Increasing the PQ concentration gives us an opportunity to realize thinner layers (<100 mum) saving high values of the diffraction efficiency. Decreasing the thickness of the layer allows higher observation angles of the received image and a wider spectral range of the incident light.

Effects of dispersion and interfacial modification on the macroscale properties of TiO 2 polymer–matrix nanocomposites

This paper quantifies how the quality of dispersion and the quality of the interfacial interaction between TiO 2 nanoparticles and host polymer independently affect benchmark properties such as glass transition temperature ( T g), elastic modulus and loss modulus. By examining these composites with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM), we demonstrate changes in properties depending on the adhesive/wetting or repulsive/dewetting interactions the nanoparticles have with the bulk polymer. We further quantify the dispersion of TiO 2 nanoparticles in polymethylmethacrylate (PMMA) matrices by a digital–optical method and correlate those values to the degree of T g depression compared to neat PMMA. Samples with the same weight percent of nanoparticles but better dispersion show larger shifts in T g.

Manifestation of second-order nonlinear optical effects in KTP and RTP nanocrystallites incorporated into polymer matrices

Strong second-order optical effects in KTiOPO 4 (KTP) nanocrystallites incorporated into polymethylmethacrylate (PMMA) matrices have been found. The maximally achieved value of the effective second-order susceptibility was equal to about 2.2 pm/V at laser wavelength 1320 nm and at liquid helium temperature (LHeT). It corresponds to concentration of the nanocrystallites of about 5.6% in weighting units. Incorporation of Rb ions and finally conversion to RbTiOPO 4 (RTP) nanocrystallites substantially reduces the effect. A similar decrease is observed when the PMMA matrix is replaced by polyvinylcarbazole (PVK) matrix.

Measurement of nonlinear properties and optical limiting ability of Rhodamine6G doped silica and polymeric samples

The third order nonlinear optical properties of Rhodamine6G (Rh6G) doped silica and polymeric samples have been investigated using single beam z-scan technique under excitation by the second harmonic of Nd:YAG laser beam (532 nm). The nonlinear refractive index, nonlinear absorption coefficient, real and imaginary parts of third order nonlinear susceptibility in the samples of silica and poly-methylmethacrylate (PMMA) matrices are measured. Thermal contribution to the nonlinear refractive index in case of undoped silica samples has been calculated in order to have better accuracy of the material response contribution to third order nonlinearity. The comparative study of the optical limiting performance of Rh6G doped silica and polymeric samples show that Rh6G doped silica is relatively superior for optical limiting applications.

Dielectric relaxation of (N(C2H5)4)2CoCl2Br2 nanocrystallites incorporated into the PMMA matrix

The dielectric properties of tetraethylammonium dibromo-dichloro-cobaltate (N(C2H5)4)2CoCl2Br2 (TEA-CBC) nanocrystallites incorporated into the polymethylmethacrylate (PMMA) matrix were investigated within the spectral range of 3×105–3×109Hz in the temperature range of 90–300K. The considerable difference of the dielectric spectra of the nanocomposite compared to the TEA-CBC crystal and to the pure PMMA matrix was observed. The phenomenon of the ‘negative capacity’ has been found in the considered material. Its dependence on the NC content was investigated. Temperature investigations of the dielectric permittivity for the TEA-CBC NC incorporated into the polymer PMMA matrices have shown the sharp-like resonance dependences of the imaginary part of the dielectric permittivity near 1.2GHz. The intensity of the corresponding resonance peaks increase sub-linearly with increasing NC content. Taking into account the substantial growth of the imaginary part of the permittivity with increasing NC concentration, one can assume that the main contribution to the effect is given by the interface NC-PMMA regions. Additional experiments were performed to eliminate the influence of ‘geometry factor’.

Optically induced linear electro-optic effects in ytterbium-doped strontium yttrium borate Sr3Y(BO3)3:Yb nanocrystallites incorporated into polymer matrices

Yb-doped Sr3Y(BO3)3 nanocrystallites incorporated into polymethyl methacrylate matrices (4.5% by weight) were optically treated by coherent picosecond laser pulses at 1.34 and 0.67μm. This composite exhibits a large effective electro-optic coefficient (up to 6.2pm∕V at 1040nm wavelength). Decrease of the nanocrystallite size and increase of the Yb content lead to substantial enhancement of the effective electro-optic coefficient. For nanocrystallite sizes equal to about 5nm, the coefficient increases from 2.2pm∕V (8% of Yb) up to 6.2pm∕V (20% of Yb). This material appears thus promising in application for the optically operated modulators.

Role of microenvironment in the mixed Langmuir–Blodgett films

This paper reports the π– A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir–Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). π– A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV–vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.

Langmuir–Blodgett films of 9-phenyl anthracene molecules incorporated into different matrices

This communication reports the surface pressure ( π) versus area per molecule (A) isotherm characteristics of the mixed films of 9-phenyl anthracene (PA) in stearic acid (SA) and polymethyl methacrylate (PMMA) matrices, at the air–water interface. The mixed Langmuir films at the air–water interface have been observed to be easily transferred onto solid substrates to form uniform Langmuir–Blodgett films. By changing various parameters, namely molefraction, surface pressure of lifting and number of layers, the mixed Langmuir–Blodgett (LB) films of various types have been fabricated successfully and their spectroscopic characteristics have been reported. From the isotherm characteristics and the area per molecule versus molefraction plot, it is evident that the PA molecules are successfully incorporated into mixed Langmuir–Blodgett films. UV–vis absorption spectroscopic study of the mixed LB films at various molefractions of PA in two different matrices reveal that formation of I-type aggregate in PMMA matrix whereas both I- and H-type aggregates are playing their dominant role in SA matrix. Moreover, fluorescence spectroscopic study reveals reabsorption effect. Molecular movement persists in the freshly prepared LB films, as is evident from the time dependent changes in both UV–vis absorption and fluorescence spectra of the mixed LB films in both matrices. From our observation it is evident that about 200 h is required to get the LB films in a stable condition. Dimers and higher order n-mers are formed at a higher surface pressure of 30 mN m −1.

Recording of dynamic holograms by nanosecond and picosecond laser pulses in solid-state fullerene-containing matrices

The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms.

High-precision thermal conductivity measurements as a probe of polymer/nanoparticle interfaces

We use the 3ω method to study the thermal conductivity of composites of nanoscale alumina particles in polymethylmethacrylate (PMMA) matrices. Effective medium theory and data for the changes in conductivity produced by low volume fractions of particle fillers are used to estimate the thermal conductance G of PMMA/alumina interfaces in the temperature range of 40&amp;lt;T&amp;lt;280 K. Near room temperature, G≈30±10 MW m−2 K−1 and the critical particle radius, r0=Λ0/G, is extremely small, r0≈7.5±2.5 nm. (Λ0=0.205 W m−1 K−1 is the conductivity of the PMMA matrix.) Therefore, high volume fractions of typical ceramic nanoparticles with r≫r0 can be used in thermal interface materials such as adhesives, pastes, and pads.

Energy transfer in Rh 6G:Rh B system in PMMA matrix under cw laser excitation

Energy transfer of Rh 6G:Rh B dye–mixtures in a poly methyl methacrylate (PMMA) matrix was studied by investigating the emission spectral characteristics under argon ion laser excitation. The fluorescence behaviour of the acceptor dye (Rh B) was investigated for various concentration of the donor (Rh 6G) and excitation powers. The energy transfer rate constants ( k f), transfer probability ( P da) and the transfer efficiency ( η) have been evaluated and their concentration dependence on donor molecules was studied. The observed decrement in the emission peak wavelength of the acceptor dye with donor concentration is attributed to the formation of complexes in the dye–mixture and also to the result of cross-relaxation taking place in the donor dye system. The blue shift in the emission wavelength of the acceptor was also investigated for various donor concentrations. A significant enhancement of fluorescence intensity of the acceptor (Rh B) of the order of 226% and a transfer efficiency of 90% were observed in the present dye–mixture system as compared with pure Rh B, both in PMMA matrices. Further the experimental results revealed the non-radiative type energy transfer for the dye system in the PMMA matrix.

Steady state and time-resolved spectroscopic studies of 7-hydroxyquinoline in various polymeric matrices

The photophysical behavior of 7-hydroxyquinoline (7HQ) is studied in four polymer matrices, viz. polymethyl methacrylate (PMMA), cellulose acetate (CA), polyvinyl alcohol (PVA) and Nafion®-117, at ambient temperature using both steady state and time-domain measurements. The study reveals both ground as well as excited state tautomerization in the case of PVA. In PMMA and CA, the intermolecular hydrogen bond to the host polymer results in proton transfer. Edge excitation red shift (EERS) and excitation and emission wavelength dependent decays are observed for normal emission in PMMA and CA matrices. These results are attributed to the trapping of a normal molecule in different geometries. In Nafion®, the results show the presence of 7HQ cationic species trapped in the polymer.

Optical studies of phthalocyanine molecules in PMMA matrix

Optical absorption and emission spectral studies of various rare earth phthalocyanine (RePc) molecules in polymethyl methacrylate (PMMA) matrix have been reported for the first time. The recorded spectra are analyzed to yield the important spectral parameters such as optical absorption cross-section ( σ a), emission cross-section ( σ e), oscillator strength ( f), dipole strength ( q), fluorescence band width (Δ λ), emission wavelength ( λ), radiative decay time ( τ) and optical gain ( G). Analysis shows that the emission cross-section and optical gain are maximum in the europium diphthalocyanine (EuH(Pc) 2)-doped PMMA matrix. A comparison of the calculated emission parameters with other polymer matrices viz. PVA and cyano acrylate, shows that they are smaller in the neodymium diphthalocyanine (NdH(Pc) 2) and samarium diphthalocyanine (SmH(Pc) 2)-impregnated PMMA matrices. The parameters are found to be improved in the PMMA matrices of lanthanum phthalocyanine (LaPc) and EuH(Pc) 2 as compared to the PVA matrix. On the other hand, these parameters greatly underestimate the values for all the PMMA-based systems as compared to the borate glassy systems.

Quantum-confined copper(I) bromide microcrystallites embedded in polymethyl methacrylate matrices

We report a new method for the preparation of copper(I) bromide (CuBr) microcrystallites embedded in polymethyl methacrylate (PMMA) films. This method takes advantage of the fact that both CuBr and PMMA dissolve in acetonitrile. The particle size is controlled by the properties of the supersaturated precursor film and its heat treatment. The precipitation process of CuBr microcrystallites was found to be different than that for oxide glass matrices.

Frequency dependence of spectral diffusion in hole-burning systems: resonant effects of infrared radiation

Light-induced spectral diffusion in photochemical hole-burning systems is investigated with respect to its dependence on the frequency of the irradiated light in the wavelength range between 2 and 5 μm. The investigated systems are protonated and deuterated polymethyl methacrylate (PMMA) matrices doped with metal-free phthalocyanine (H2Pc). Resonant hole-filling and resonant hole-broadening behaviors are found, both being caused by the excitation of local, but different, matrix vibrations. Possible mechanisms are discussed under the aspect of the excitation of IR- and Raman-active vibrations of the matrix.

Luminescence of stereoisomers of the open form of spiropyran in polymer films

Photocoloration of spyropyran in polymethyl methacrylate and polystyrene matrices at 293 and 77 K results in the formation of a set of photoproducts with individual spectral characteristics, and the structure of a certain stereoisomer was assigned to each photoproduct based on these characteristics.

Photoquenching and the relaxation recovery of naphthalene excimer fluorescence in polymethyl methacrylate matrices

Photoquenching and the relaxation recovery of naphthalene excimer fluorescence in polymethyl methacrylate matrices

Dipole moments and polarizabilities of triplet-triplet transitions of anthracene in different solvents studied by flash photolysis

Transient absorption spectra (triplet-triplet) of anthracene are observed in the vapor phase, polar and non-polar solvents, and polymethylmethacrylate matrices at room temperature. The results are compared with those of previous observations (singlet-singlet), after estimating the change in polarizability. When the width of the bands studied is plotted versus the viscosity and the dipole moments of the solvents used, straight lines are obtained.

Pressure induced spectral diffusion as investigated by linewidth studies of polymers doped with dye molecules

Photochemical hole burning at 1.5 K was used to study the influence of uniaxial pressure on the homogeneous line profile of the S 1←S 0 transition of free base phthalocyanine in polyethylene (PE) and polymethylmethacrylate (PMMA) matrices. The line profiles which were observed show already at pressure changes which were as small as 100 hPa substantial broadening effects. At higher pressures of up to 3 x 10 4 hPa we observed irreversible line broadening phenomena, which we attribute to irreversible site changes of the host-guest system.