Polymer Viscoelastic Properties Measured by Friction Force Microscopy

Hammerschmidt, Jon A.; Moasser, Bahram; Gladfelter, Wayne L.; Haugstad, Greg; Jones, Richard R.

doi:10.1021/ma9603239

Cited by 50 publications

(42 citation statements)

References 25 publications

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“…Hence, the pressure exerted by the tip cannot be considered hydrostatic. In addition, the lateral force is measured after the temperature has stabilized (20,22,(28)(29)(30). Therefore, under these isothermal conditions, the polymer can be considered incompressible, i.e.…”

Section: Resultsmentioning

confidence: 99%

Glass Transition Measurements of Ultrathin Polystyrene Films

Buenviaje

Dinelli

Overney

2000

ACS Symposium Series

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Data from various experiments suggest that the mechanical properties of thin polymer films depend, in a complex manner, on the film preparation process, in conjunction with interfacial interactions. In this paper, we discuss how and why interfacial interactions can affect the shear mechanical properties of spincoated polymer films. For example, confinement effects due to the spin coating process have been observed to exceed the nearest neighbor interaction distances by one order of magnitude. We introduce shear modulation scanning probe microscopy (SPM) as a technique to measure local shear property changes in thin polymer films as a function of temperature. Comparisons with bulk and lateral force measurements demonstrate the reliability of the technique. Using the shear modulation SPM, we observe a molecular weight dependence on the bulk glass transition. Measurements taken on polystyrene surfaces of various film thickness provide insight into how the glass transition of films are affected by substrate confinement.2

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Section: Resultsmentioning

confidence: 99%

Glass Transition Measurements of Ultrathin Polystyrene Films

Buenviaje

Dinelli

Overney

2000

ACS Symposium Series

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“…Friction force measurements are performed via scanning the tip back and forth over long distances. [8][9][10] The friction force is obtained by subtraction of the lateral forces measured in the two directions. Therefore, it is an average measurement and unknown offsets and possible influences of topography are canceled out during subtraction.…”

Section: Introductionmentioning

confidence: 99%

Investigations of heterogeneous ultrathin blends using lateral force microscopy

2001

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In order to study the glass transition of thin film polymer blends, high spatial resolution and temperature sensitivity is needed. In this paper, we emphasize the importance of the calibration of scanning parameters such as load and speed when measuring the glass transition temperature of polymers using lateral force microscopy. Once calibrated, this method is ideal for investigations of heterogeneous samples such as blends and co-polymers. We present an analysis technique for lateral force imaging using a fast and stable cooling/heating stage. This approach involves mapping the friction forces over a certain area and identifying regions of different frictional properties. The difference in the average friction force can then be plotted as a function of temperature. The friction force is expected to vary around the glass transition. Therefore, the glass transition temperature can be defined as the temperature at which the difference in the average friction force undergoes a slope change. We present investigations of blends using polystyrene mixed with poly(butylmethacrylate). The transition temperatures obtained are in good agreement with the bulk values of corresponding homopolymeric films.

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“…The frictional response is well known to have a large contribution from the viscous character of the material being imaged (17,19). Some investigators have examined response functions by characterizing friction and/or wear under repeated scanning with variable loads (13,33), providing information on the viscoelastic and viscoplastic properties of a material.…”

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confidence: 99%

Biofilm Cohesiveness Measurement Using a Novel Atomic Force Microscopy Methodology

Ahimou¹,

Semmens²,

Novak³

et al. 2007

Appl Environ Microbiol

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113

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Biofilms can be undesirable, as in those covering medical implants, and beneficial, such as when they are used for waste treatment. Because cohesive strength is a primary factor affecting the balance between growth and detachment, its quantification is essential in understanding, predicting, and modeling biofilm development. In this study, we developed a novel atomic force microscopy (AFM) method for reproducibly measuring, in situ, the cohesive energy levels of moist 1-day biofilms. The biofilm was grown from an undefined mixed culture taken from activated sludge. The volume of biofilm displaced and the corresponding frictional energy dissipated were determined as a function of biofilm depth, resulting in the calculation of the cohesive energy. Our results showed that cohesive energy increased with biofilm depth, from 0.10 ؎ 0.07 nJ/m 3 to 2.05 ؎ 0.62 nJ/m 3 . This observation was reproducible, with four different biofilms showing the same behavior. Cohesive energy also increased from 0.10 ؎ 0.07 nJ/m 3 to 1.98 ؎ 0.34 nJ/m 3 when calcium (10 mM) was added to the reactor during biofilm cultivation. These results agree with previous reports on calcium increasing the cohesiveness of biofilms. This AFM-based technique can be performed with available off-the-shelf instrumentation. It could therefore be widely used to examine biofilm cohesion under a variety of conditions.It is essential to understand biofilm stability to both encourage biofilm maintenance in some applications, such as waste treatment, and effectively remove undesired biofilm in others, as in biofilms covering medical implants. Biofilm detachment is one of the critical factors that balance growth and plays a role in the development of biofilm spatial heterogeneity. While factors responsible for biofilm growth are well studied (16,29,39,42,43), those controlling the detachment process are not clearly understood (28,36,38). As a consequence, a good understanding of the relationships between operating conditions and biofilm cohesion is lacking. The cohesive strength of the biofilm is influenced by extracellular polymeric substances (EPS) and specific compounds, such as calcium, which fill the space between microbial cells and bind cells together (23,30). Understanding the cohesive interactions in the biofilm matrix under a variety of conditions could lead to the design of new strategies for controlling biofilm development based on disrupting or protecting the matrix holding the biofilm together.Because cohesive strength is a primary factor affecting biofilm sloughing, its quantification is essential in understanding detachment. A few methods based on the use of custom devices have been proposed to investigate biofilm cohesive strength. Poppele and Hozalski (31) measured the tensile strength levels of biofilms from activated sludge by using a micromechanical device based on the deflection of a glass micropipette separating a microbial aggregate held by suction. Körstgens et al. (22) used a uniaxial compression measurement device to determine the yield st...

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Polymer Viscoelastic Properties Measured by Friction Force Microscopy

Cited by 50 publications

References 25 publications

Glass Transition Measurements of Ultrathin Polystyrene Films

Glass Transition Measurements of Ultrathin Polystyrene Films

Investigations of heterogeneous ultrathin blends using lateral force microscopy

Biofilm Cohesiveness Measurement Using a Novel Atomic Force Microscopy Methodology

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