High resolution, high speed multi-frequency dynamic study of visco-elastic properites

Patent metadata

Field	Value
Publication number	US-9417170-B2
Application number	US-201213550344-A
Country	US
Kind code	B2
Filing date	Jul 16, 2012
Priority date	Jul 15, 2011
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

The present invention provides an apparatus and method including hardware and software, which allows collecting and analyzing of data to obtain information about mechanical properties of soft materials. This allows surface mapping of viscoelastic properties in a high-resolution and fast manner. It also allows finding the degree of nonlinearity of the material response of the sample during the measurements. The apparatus can be used as a stand-alone device, or an add-on to either the existing atomic force microscope or nanoindenter device.

First claim

What is claimed is:

1. A method for fast, high-resolution mapping of a mechanical property of a viscoelastic surface, the method comprising the steps:
applying an indenting probe to a first indentation depth on the viscoelastic surface;
generating an oscillatory signal comprising the sum of a first set of at least two different predefined frequencies;
generating mechanical oscillations of said viscoelastic surface using said oscillatory signal;
measuring, at said predefined frequencies, a viscoelastic parameter at said first indentation depth, wherein the step of measuring a viscoelastic parameter at said first indentation depth comprises: (i) measuring, at said predefined frequencies, a first viscoelastic parameter at said first indentation depth of said viscoelastic surface, wherein said first viscoelastic parameter is a storage modulus and/or a loss modulus; and (ii) sequentially measuring, for each of said first set of at least two predefined frequencies included in said sum, a second viscoelastic parameter at said first indentation depth of said viscoelastic surface; and
analyzing the measurement to determine said property of the viscoelastic surface;
wherein the viscoelastic parameter is measured immediately after applying the indenting probe without waiting for viscoelastic creep relaxation of said viscoelastic surface.

2. The method of claim 1 , wherein the generated oscillatory signal is used to generate mechanical oscillations of the indenting probe.

3. The method of claim 1 , wherein the step of analyzing the measurement to determine said property of the viscoelastic surface comprises calculating a difference between said first viscoelastic parameter and said second viscoelastic parameter at one of said predefined frequencies, wherein said difference is proportional to the degree of non-linearity of the mechanical response of said viscoelastic surface.

4. The method of claim 1 , wherein positioning of said indenting probe is electrically controlled by a controller of an atomic force microscope.

5. The method of claim 1 , wherein positioning of said viscoelastic surface is electrically controlled by an external controller.

6. The method of claim 1 , wherein the values of said at least two different predefined frequencies are not multiples of each other.

7. The method of claim 1 , further comprising the step of measuring said viscoelastic parameter at a second indentation depth.

8. The method of claim 1 , further comprising the step of measuring said viscoelastic parameter at a frequency different from said first set of at least two different predefined frequencies.

9. The method of claim 1 , wherein said first viscoelastic parameter is selected from the group consisting of viscoelastic creep, non-linearity of the mechanical response of said viscoelastic surface, mathematical functions of storage and/or loss moduli taken at different predefined frequencies and several indentation oscillation amplitudes of said mechanical oscillations, and combinations thereof.

10. The method of claim 1 , wherein said first and second viscoelastic parameters of said viscoelastic surface are measured using a nanoindenter or an atomic force microscope.

11. A system for fast, high-resolution mapping of a mechanical property of a viscoelastic surface of a sample, the system comprising:
a signal generator, said signal generator adapted to generate a first oscillatory signal comprising the sum of a first set of at least two different predefined frequencies, wherein said generated oscillatory signal is transferred to said viscoelastic surface;
a computer in communication with said signal generator and configured or programmed to send a signal directing said signal generator to generate said oscillatory signal;
a mechanically oscillating scanner electrically coupled to said signal generator and adapted to have said sample mounted thereon, wherein the mechanically oscillating scanner is adapted to mechanically oscillate according to said generated oscillatory signal;
a cantilevered probe adapted to engage the viscoelastic surface when said sample is mounted on said mechanically oscillating scanner, wherein said cantilevered probe comprises a position detector configured to detect the position of the cantilevered probe on the viscoelastic surface; and
a recording unit adapted to measure a viscoelastic parameter of said viscoelastic surface, the recording unit comprising a first input electrically coupled to said scanner, a first output electrically coupled to said scanner, and a second output electrically coupled to the position detector of said cantilevered probe, wherein said first input and said first and second outputs are electrically coupled to said computer;
wherein said viscoelastic parameter is measured immediately after the cantilevered probe engages the viscoelastic surface, without waiting for viscoelastic creep relaxation of said viscoelastic surface.

12. The system of claim 11 , wherein positioning of said cantilevered probe is controlled by an atomic force microscope.

13. The system of claim 11 , wherein positioning of said viscoelastic surface is electrically controlled by an external controller.

14. The system of claim 11 , wherein said scanner is a piezoelectric scanner.

15. The system of claim 11 , wherein said signal generator is further adapted to generate multiple sinusoidal signals together with a DC shift, and transmit said generated DC shift and multiple sinusoidal signals to said scanner.

16. The system of claim 11 , wherein the values of said at least two different predefined frequencies are not multiples of each other.

17. The system of claim 11 , wherein said first viscoelastic parameter is selected from the group consisting of creep, non-linearity of the mechanical response of said viscoelastic surface, mathematical functions of storage and/or loss moduli taken at different said predefined frequencies and several indentation oscillation amplitudes of said mechanical oscillations, and combinations thereof.

Assignees

• Sokolov Igor
• Dokukin Maxim Evgenevich
• Univ Clarkson

Inventors

• Sokolov Igor
• Dokukin Maxim Evgenevich

Classifications

• G01Q60/366

  Nanoindenters, i.e. wherein the indenting force is measured · CPC title

• G01N2203/0218

  Calculations based on experimental data · CPC title

• G01N3/32 Primary

  by applying repeated or pulsating forces · CPC title

• G01N2203/0094

  Visco-elasticity · CPC title