Application Note | Adhesion Testing

Adhesiveness of Tape via Nanoindentation

Quantifying Adhesive Tack from the Negative Force and Work of Indenter Pull-Off

Adhesive tape rolls and a load-depth curve

Research & Experimental Testing

Frank Liu

Visual Design & Editorial

Andrew Shore

Introduction

The effectiveness of tape is determined by its cohesive and adhesive abilities. Cohesion is defined as the tape’s internal strength while adhesion is the tape’s ability to bond to its interacting surface. The adhesion of tape is influenced by numerous factors, such as exerted pressure, surface energy, molecular forces, and surface texture [1]. To quantify adhesion of tapes, nanoindentation with the NANOVEA Mechanical Tester’s Nano Module can be conducted to measure the work required to separate the indenter from the tape.

Importance of Quantifying Adhesion of Tape with Nanoindentation

Replicating real life situations, such as skin and band-aid or tire and asphalt interaction, can be quite important for quality control or R&D research. The NANOVEA Mechanical Tester can accommodate them to create ideal conditions with its ability to output normal forces below 1mN and up to 200N. Environmental testing can also be conducted with humidity, temperature, and lubrication modules. This can be used to find optimal conditions for maximizing adhesion or to find factors that limit the effectiveness of the adhesive.

Measurement Objective

The adhesion of three types of adhesive tapes were quantified using NANOVEA’s Mechanical Tester’s Nano Module. By indenting in the sample, the sample will stick onto the indenter surface and apply a negative force when the indenter is raised above the sample surface. Eventually, the distance between the sample and the indenter will be too great and the indenter will separate from the sample, leaving a near-zero force reading. The negative force region is used to quantify adhesion since it is caused by the tape “holding onto” the indenter.

NANOVEA PB1000 Large Platform

Mechanical Tester

Nanoindenter and scratch tester platform NANOVEA PB1000 with nano and micro modules

Test Conditions and Procedures

The following indentation parameters were used:

Parameter (all samples)Value
Maximum force1 mN
Loading rate2 V/min
Unloading rate10 V/min
Creep2 s
Indenter typeFlat
Indenter radius50 µm

Table 1: Indentation parameters.

The loading rate of 10 V/min is approximately 200µm/min.

It is important to note that the numbers obtained are heavily related to the indentation parameters set. Changing the amount of pressure applied into the sample, how long the indenter is in the sample, or how fast the indenter is removed can change the adhesive properties.

Results

Below is a summary of results from the nanoindentation tests conducted on three different tape samples. The work was calculated by integrating the region where the load was negative. The work is representative of how much energy is required to completely separate the tape and the indenter.

TapeMaximum negative force (mN)Work (nJ)
Tape 10.960 ± 0.105101.30 ± 11.26
Tape 20.438 ± 0.01332.24 ± 3.24
Tape 30.343 ± 0.01811.23 ± 1.77

Table 2: Summary of the adhesion results.

Tape 1

TestMaximum negative load (mN)Work (nJ)
11.137120.07
20.962105.99
30.992100.06
40.87187.89
50.83792.45
Average0.960101.29
Standard deviation0.10511.26

Table 3: Nanoindentation results for Tape 1.

Load versus depth curve for Tape 1, with the load turning negative as the indenter is withdrawn
Fig. 1: Load vs depth for Tape 1.

Tape 2

TestMaximum negative load (mN)Work (nJ)
10.43632.13
20.45236.45
30.42729.84
40.45335.08
50.42227.68
Average0.43832.24
Standard deviation0.0133.24

Table 4: Nanoindentation results for Tape 2.

Load versus depth curve for Tape 2, with the load turning negative as the indenter is withdrawn
Fig. 2: Load vs depth for Tape 2.

Tape 3

TestMaximum negative load (mN)Work (nJ)
10.33010.29
20.33011.04
30.33911.26
40.37914.44
50.3389.11
Average0.34311.23
Standard deviation0.0181.77

Table 5: Nanoindentation results for Tape 3.

Load versus depth curve for Tape 3, with the load turning negative as the indenter is withdrawn
Fig. 3: Load vs depth for Tape 3.

Discussion

All three tapes displayed different adhesive strengths. Tape 1 was significantly stronger than tape 2 and 3. The work required to remove the Tapes 1, 2, and 3 were 101.29 ± 11.26, 32.24 ± 3.24, and 11.23 ± 1.77 nJ respectively. While the standard deviation is quite large (possibly due to surface contaminants and inhomogeneous surfaces), the numbers obtained are distinct. This shows that the NANOVEA Mechanical Tester Nano Module was able to successfully find differences in adhesion between three tape samples.

Conclusion

With the NANOVEA Mechanical Tester’s Nano Module, the adhesion of three different tape samples were obtained. The samples had distinct adhesion properties and can be ranked from strongest to weakest adhesion: Tape 1, Tape 2, and Tape 3. This type of testing is applicable to all types of material (e.g. biological, polymers, and others) as long as the material can adhere to its opposing surface. With the NANOVEA Mechanical Tester’s ability to sense forces below 1mN, it can even perform very sensitive measurements for unique applications.

References

“What exactly is the physical or chemical process that makes adhesive tape stick?” Scientific American, https://www.scientificamerican.com/article/what-exactly-is-the-physi/

Frequently Asked Questions About Tape Adhesion Testing

How can nanoindentation measure tape adhesion?

A flat indenter is pressed into the tape and withdrawn. The tape sticks to the indenter and pulls on it, giving a negative force until the two separate; that negative-force region quantifies adhesion.

What is the pull-off work?

The work is calculated by integrating the region where the load is negative. It represents how much energy is required to completely separate the tape and the indenter.

What did the three tapes measure?

Tape 1 needed 101.29 ± 11.26 nJ to separate (maximum negative force 0.960 ± 0.105 mN), Tape 2 32.24 ± 3.24 nJ and Tape 3 11.23 ± 1.77 nJ, ranking the tapes from strongest to weakest adhesion.

Do test parameters change the result?

Yes. The numbers are heavily related to the indentation parameters: the pressure applied, how long the indenter stays in the sample and how fast it is removed can all change the adhesive properties measured.

Can real-life conditions be simulated?

The Mechanical Tester outputs normal forces from below 1 mN up to 200 N, and humidity, temperature and lubrication modules allow environmental testing, for example to replicate skin and bandage or tire and asphalt contact.

Which materials can be tested this way?

All types of material, such as biological materials and polymers, as long as the material can adhere to its opposing surface.

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