Albert E. Kamanyi

Characterization of polymer thin films by phase-sensitive acoustic microscopy and atomic force microscopy: a comparative review

The potential of phase‐sensitive acoustic microscopy (PSAM) for characterizing polymer thin films is reviewed in comparison to atomic force microscopy (AFM). This comparison is based on results from three‐dimensional vector contrast imaging and multimodal imaging using PSAM and AFM, respectively. The similarities and differences between the information that can be derived from the AFM topography and phase images, and the PSAM phase and amplitude micrographs are examined. In particular, the significance of the PSAM phase information for qualitative and quantitative characterization of the polymer films is examined for systems that generate surface waves, and those that do not. The relative merits, limitations and outlook of both techniques, individually, and as a complementary pair, are discussed.

Age-Dependent Acoustic and Microelastic Properties of Red Blood Cells Determined by Vector Contrast Acoustic Microscopy

Variations of the mechanical properties of red blood cells that occur during their life span have long been an intriguing task for investigations. The research presented is based on noninvasive monitoring of red blood cells of different ages performed by scanning acoustic microscopy with magnitude and phase contrast. The characteristic signature of fixed cells from groups of three different ages fractionated according to mass density is obtained from the acoustic microscope images, with the data represented in polar graphs. The analysis of these data enables the determination of averaged values for the velocities of ultrasound propagating in the cells from the different groups ranging from (1,681 ± 16) m s(-1) in the youngest to (1,986 ± 20) m s(-1) in the oldest group. The determined bulk modulus varies with age from (3.04 ± 0.05) GPa to (4.34 ± 0.08) GPa. An approach to determine for an age-mixed population of red blood cells, collected from a healthy person, the age of the individual cells and the age dependence of the cell parameters including density, velocity, and attenuation of longitudinal polarized ultrasonic waves traveling in the cells is demonstrated.

Advances in phase-sensitive acoustic microscopy studies of polymer blend films: annealing effects and micro-elastic characterization of PS/PMMA blends

The unique phase‐sensitive acoustic microscope is used for the structural and mechanical characterization of thin films of polystyrene/polymethylmethacrylate blends. The effect of annealing on blends of polystyrene/polymethylmethacrylate spin coated from different solvents unto a substrate is studied. Varying the solvents according to vapour pressure and spin coating at different speeds (for thickness variation) led to changes in phase domain distributions and overall structural properties before annealing. Annealing in vacuum at 190°C for 48 h resulted in the elimination of solvent effects with all samples reverting to a similar morphology irrespective of common solvent and thickness. The Youngs moduli at specific points on the film (Epolystyrene= 3.4 ± 0.3 GPa, Epolymethylmethacrylate= 4.2 ± 0.4 GPa) and over a given area (Epolystyrene/polymethylmethacrylate= 3.9 ± 0.4 GPa) were determined by combinatory use of the atomic force microscope and phase‐sensitive acoustic microscope. These results demonstrate a minimally invasive method for the quantitative characterization of polymer blend films.

Determination of mechanical properties of layered materials with vector-contrast scanning acoustic microscopy by polar diagram image representation

Microscopic objects including living cells on a planar substrate are investigated in bio-medical applications of scanning acoustic microscopy. Beside of the observation of lateral structures, the determination of sample properties such as density, sound velocity, and attenuation is desired, from which elastic properties can be derived. This can be achieved with the aid of the acoustic phase and magnitude contrast represented in a polar plot. For homogeneous and sufficiently planar objects the contrast in magnitude and phase is a function of the properties of the substrate and the coupling fluid, which both can easily be determined, and of the mechanical properties of the sample under observation. For observation in reflection and variable thickness of the sample the signal will depend on the actual thickness. This signature of the object can be fitted based on a conventional ray model for the sound propagating in the coupling medium and the sample. The model includes also the refraction and reflection at all interfaces between transducer, lens material, coupling fluid, object, and substrate. The method is demonstrated for a chitosan film deposited on a glass substrate. The scheme presented here is capable to reach a resolution of about and even below 1% for relevant quantities in applications involving imaging at 1.2 GHz in aqueous coupling fluids.

Effects of solvent vapor pressure and spin-coating speed on morphology of thin polymer blend films

Thin films of polystyrene (PS)/polymethylmethacrylate (PMMA) blends were made by casting from solutions with solvents of varying vapor pressure. Solvents used were chloroform, toluene and dichloromethane. Spin coating was carried out at varying speeds yielding films of different thickness. Atomic force microscopy and phase-sensitive acoustic microscopy were used to investigate the effects of spin speed and solvent vapor pressure on morphology. The domains formed due to lateral phase separation proved to be strongly influenced by vapor pressure with completely different surface structures for the three solvents. The films cast from high vapor pressure solutions displayed an increased surface roughness. Surface morphology is explained by the relative solubility in the different solvents, surface affinity, spin speed and viscosity.

Ultra-High Resolution Thin Film Thickness Delineation Using Reflection Phase-Sensitive Acoustic Microscopy

The acoustic phase and magnitude data of a planar homogenous sample of smoothly varying thickness deposited on a glass substrate can best be represented by a polar plot. In this work, the method is extended to achieve topographical mapping of thin films with a height resolution beyond the diffraction limit of optical confocal microscopy. The radial dependence of the polar graph describes the regression of the magnitude of the reflected signal due to the attenuation. The later increases with the gradual increase of the thickness and is additionally influenced by interference effects. The angular dependence of the polar plot reveals the rotation of the phase angle of the signal due to reflection from different thicknesses of the sample. Model calculations are employed, and input values are varied until an optimum agreement with the measurement data points is achieved and the primary acoustic properties (speed of longitudinally polarized ultrasound, mechanical density of the sample and the attenuation within the material) are obtained. The model manifests the variation of the magnitude and phase of the reflected signal due to variation in thickness. After optimum adjustment of the model parameters, the thickness corresponding to each measured value of the reflectivity is obtained.

Determination of sound velocity and acoustic impedance of thin chitosan films by phase-sensitive acoustic microscopy

The biomaterial chitosan is used in the paper manufacturing industry, as a wound healing agent and in filtration amongst others. In this paper the longitudinal sound velocity and acoustic impedance of thin films of chitosan of varying thicknesses are determined by vector-contrast acoustic microscopy. The exploitation of the relative reflectivity information from the maximum amplitude images and a comparison of the experimentally obtained V(z) curves with simulations using appropriate models are applied for the evaluation of the sound velocity. These results were compared to those previously obtained results with the same instrument.

Soft matter Acoustics: Non-destructive health monitoring of polymer blend films

Soft matter acoustics is concerned with the application of acoustical techniques in the study of soft matter. In this paper, we demonstrate the use of phase sensitive acoustic microscopy (PSAM) in synchronous mapping of threedimensional heterogeneity of sample soft matter systems: thin film blends of polystyrene (PS) and poly (methylmethacrylate) (PMMA). The use of acoustic phase contrast imaging for cure or health monitoring of polymer systems is discussed.

Combinatory scanning confocal laser and acoustic vector contrast microscopy: multi-contrast imaging of soft matter samples

Synchronous operation of a confocal laser scanning microscope (CLSM) and a confocal vector contrast scanning acoustic microscope (phase sensitive scanning acoustic microscopy: PSAM) has been developed. Imaging is performed on objects mounted on a cover slide with the CLSM operated in reflection through the slide with an immersion fluid and PSAM operating in water respectively aqueous solutions from the other side (half space). Examples involving living cells and soft matter samples illustrating various combinatory schemes and advantages of multi-contrast optical and acoustic contrast are demonstrated. This includes combinations with fluorescence microscopy and ultrasonic topographical imaging as well as combinatory three-dimensional imaging.

Characterization of malaria infected blood cells by scanning confocal laser and acoustic vector contrast microscopy

Acoustic and optical multiple contrast microscopy has been employed in order to explore characterizable parameters of red blood cells, including cells infected by the parasite Plasmodium falciparum, in order to investigate cellular modifications caused by the infection and to identify possible detection schemes for disease monitoring. Imaging schemes were based on fluorescence, optical transmission, optical reflection, and amplitude and phase of ultrasound reflected from the cells. Contrast variations observed in acoustic microscopy, but not in optical microscopy, were tentatively ascribed to changes caused by the infection.