Derek R. Oberreit1,*, David Blackford1, Gary van Schooneveld2, Seongho Jeon3

1Fluid Measurement technologies Inc., White Bear Lake, MN 551102CT Associates, Eden Prairie, MN 55455

3Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55344

AbstractDispersion of colloid nanoparticles into an aerosol first

requires nebulization of the colloid into fine droplets and

subsequent evaporation of the solvent from them. Following

solvent evaporation, droplets that did not contain a colloid

particle form particles composed of non-volatile solvent

residue. Droplets that do contain colloid particles result in

aerosolized colloid particles with a coating of non-volatile

residue. To reduce the interference by non-volatile residue

particles as well as effect on the colloid particle properties

(surface chemistry, size), it is desirable to create droplets

containing a low volume of solvent. This is especially true for

aerosolization of nanoparticles that approach the size of the

non-volatile residue particles. Nebulization is typically

accomplished using either pneumatic or electrospray methods.

While electrospray methods do provide sufficiently small

droplets (~0.3 µm), there are several limitations to the method

including poor long term stability and necessity for a

conductive solvent. Common pneumatic nebulizers create

droplet distributions with a peak diameter near 2.0 µm which

leads to a significant amount of non-volatile residue

interference in the aerosol. We present a new commercially

available pneumatic nebulizer that is designed to produce a

high number concentration of small droplets with a peak

diameter less than 0.5 µm. We compare the performance of

this nebulizer with existing aerosolization methods for a variety

of colloids. We also show additional applications of this device

for monitoring colloid concentrations in dilute systems such as

ultrapure water systems and in liquid filter efficiency testing.

Instrument Design

Introduction

Online Dilution

• Maximum non-volatile residue 1 ppm (typical of many HPLC

grade solvents)

• Less than 0.1% change in 10 nm particle diameter due to

residue

• Minimal interference by particles consisting of only NVR

Nebulizer Geometry•High purity materials of construction - minimize additional

NVR contribution

•Swept flow paths - minimize dead spaces

•Confined air-liquid mixing area – Transfer maximum gas

energy into breakup of liquid

•Ball end inertial impactor – Large droplet removal

Results

A Nanoparticle Nebulizer for Generation of Aerosolized Colloid Particles with Reduced Influence by Non-Volatile Residue

• The properties of particles in hydrosols (colloids) are

commonly measured by dispersing the colloid particles into a

gas (aerosolization)

• Primary methods for aerosolization include Nebulization

(pneumatic spraying of colloid) and Electrospray

(electrohydrodynamic spraying)

• Electrospray is not suited for all colloids and are anecdotally

unstable over long periods

• Nebulization using traditional devices typically creates

droplets on the order of 2 µm

• Non-volatile residue (NVR) in the solvent creates a particle

which is proportional to the diameter of the droplet

• As colloid particle sizes approach the size of the residue

particles, the resulting aerosol particles no longer represent

the particles in it

• Goal: Design a pneumatic nebulizer which reduces the effect

of non-volatile residue on the resulting aerosol

Nebulized Droplet Distribution•Significant reduction of the peak droplet diameter

•Leads to reduced non-volatile residue interference

• Online dilution of sample will lower the peak diameter of non-

volatile residue particles• Minimizes contamination from sample vials

• Useful to lower NVR resulting from stabilizers with minimal

coagulation due to short diluted residence time.

DispersionParticles in

SuspensionEvaporation

DispersionParticles in

SuspensionEvaporation Diameter

Peak Shift

Traditional

nebulizer

1 ppm non-volatile residue With 20 nm particle

25% Increase

in size

<0.1%

Increase in

size

2 nm

20 nm

Model 7788

nebulizer

Plumbing and Electrical•Evaporator and nebulizer temperature control

•Monitor Sample pressure and temperature

•Sample taken from pressurized stream or injected directly

Liquid Filter Testing• Nanoparticle nebulizer output particle concentration measured using a condensation particle counter with a 50% detection

efficiency at 10nm

• Downstream cumulative (>10 nm) colloid particle concentration

measured throughout filter challenge

LiquiTrak® Model 7788 Nanoparticle Nebulizer

•Manufactured by Fluid

•Measurement Technologies Inc.LiquiTrak®

Liquid Nanoparticle Sizer (LNS)•Model 7788

•Model 7780 LNS Dilution Module

•Scanning Mobility Particle SizerPatent US 8,272,253, US 8,573,034, US 7,852,465

Aerosolization of colloid particles•Aerosol size distribution measured with a Scanning Mobility

Particle Sizer (LNS system)

•Good agreement shown between aerosol particle size

distribution and colloid size distribution

Fractional coverage (Monolayers)

0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200

Re

ten

tio

n (

%)

0

20

40

60

80

100

Silica

PSL

Gold

30 nm Rated Water Filter Challenged with 2E8 #/ml ( 6ppm) 30nm Particles

8 10 12 14 16 18

Fra

cti

on

(%)

0.0

0.1

0.2

0.3

0.4

0.5

10 12 14 16 18 200.0

0.1

0.2

0.3

Colloidal particle size distribution

10nm AuNp 15nm AuNpMean 11.71 nm

Mode 12.00 nm

Mean 15.76 nm

Mode 15.00 nm

Size(diameter, nm)

6 7 8 9 20 30 40 5010

dN

/dlo

gD

p

0

2000

4000

6000

8000

10000

12000

Size(diameter, nm)

6 7 8 9 20 30 40 50 60100

2000

4000

6000

8000

10000

12000

1400010nm AuNp

Dilution ratio

1000

15nm AuNp

Dilution ratio

500

Mode 13.1 nm Mode 16.8 nm

Aerosol particle size distribution

Primary particle size (nm, log scale)

Primary particle size (nm, linear scale)

Normalized 10:1(mass ratio) TiO2/calgon size dsitributions with different dilution ratios

Size(nm, log scale)

6 7 8 15 30 40 50 60 70 80 15010 100

Y/Y

ma

x

0.0

0.2

0.4

0.6

0.8

1.0

1.2

500

1000

2000

5000

10000